Ok let me just start off by saying: Yes I know that there are multiple other Portal Cake tutorials out there but mine doesn't go bad or any of that. In fact, when you're dead it might still be alive!
Also I should warn you that this is an extremely time consuming process and you should probably get it done while it's still kind-of hot outside. Mine took me about 2 weeks to finish but you can probably cut it down to about 2-3 days. Probably more like 5 though. And one more thing, when you're done, the cake won't be edible.

Step 1: Materials

Ok this is probably one of the hardest/most time consuming food Instructables ever and you need a lot of stuff.

For The Cake*: 2 chocolate cake mixes. (You will have extra so you might also make Portal Cupcakes. Or you can eat the batter cause thats what I did.)
Whatever It Says You Need For The Mix
Cake Leveler/Knife
1 or 2 Nine Inch Round Cake Pans (You're making 2 cakes)
Old t-shirt or long piece of cloth (Recommended)

For The Outside Stuff: 1-2 Tubes of Loctite White Adhesive Caulk (better safe than sorry! go for 2 tubes of the stuff)
Caulking Gun
1 Big Birthday Candle (You can look at the actual picture and decide)
1 Box Chocolate Rice Crispies (I recommend the cheapest brand)
Plastic Knife (Optional)
Gloves (Recommended)
Fake cherries (I found some in the Home section of Target)
1 Bottle of Espresso Brown Satin Finish Spray Paint (Lowes or Home Depot I think)
1 Bottle of Spray Lacquer
A Medium Size Phillips Head Screw Driver
A bunch of spare time.

The Base:
1 Bottle of White Spray Primer
1 Bottle of Orange Spray paint
Scalloped Cake Base Things (Descriptive right? I got mine and Joanns and you can decide on the size. You should probably go for the medium/smaller size.)

* Alternatively you can use the polymer cake method. I didn't because I didn't see it until the day before I published this. Using the polymer cake method bypasses steps 2 and 3.

Step 2: The Cake Part 1

If you have an old t-shirt cut a long strip of it so you can tie it around the cake pan and then get it wet; should be pretty wet. If you have a long piece of cloth lying around you can use that instead. Tie the wet piece of cloth around the cake pan. This will keep the cakes from doming most of the time. Next just follow all the instructions on the box as far as how to make the cake. If your cakes appear still come out domed wait for it to cool and just use your cake leveler or knife to make it flat.
You can put it right in the oven, just try not to set the pan on the end strips of cloth. Also if you don't get it wet enough, it might catch on fire but that has never been a problem before.

Step 3: The Cake Part 2/ Dehydration

Now you need to get most of the water out of your cake. There are 2 methods. You can leave it out for a week or so and let it dry naturally, but that took too long for me. Alternatively, you can use method 2.
Method 2: Set your oven to its lowest temperate on convection bake, you can use regular bake if you don't have that setting. Then place the first of your cakes in the oven for 4~6 hours. Use a wooden chopstick/skewer to poke the cake, it should be difficult or impossible to puncture when it's done. Another test is if you pick it up by only one side it shouldn't break in half.
After that cake is finished make sure to put it in a dry area, or better yet if you have 2 ovens, just put it in the other one. Repeat the process on the second cake. Note that you should never put 2 cakes in the same oven because they will absorb eachothers' moisture!

Step 4: Sealing the Cakes

After you dehydrated your cakes leave them in the oven to cool. If you're impatient like me, you can take them out as soon as you think you could hold it without burning yourself. If you have those latex gloves go ahead and put them on; now spray the ENTIRE CAKE with a layer of the spray paint I mentioned earlier in the materials list. Set it outside to dry for about 20 minutes then spray it with a coating of the lacquer. Wait until it's dry enough to handle then repeat the process.

Step 5: Frosting the Cakes

Decide on which cake is going to be your base. Put a decent amount of caulk on top of that cake (you can spread it with the plastic knife if you want) then set the other cake on top of that. After waiting about 2 hours for the caulking to dry, repeat step 4 on the cake. Make sure, if you didn't already, to spray the bottoms. I like to wait a day to really give the caulking a chance to set before continuing.
Now, working quickly, spread some caulking over the top of the cake. Then take as many handfuls of rice crispies as you need and press them on so they cover the top. Repeat the process on the sides of the cake, I recommend going in sections.
Once that's all done just go around and blow off any loose crispies and fill in the areas that still look empty. Now you really should wait another day for the entire cake to dry.
You will want to stick a nail in the hole you make in the caulking tube so you can use it in a later step.
Should look about like this.

Step 6: Making the Base

Take your scalloped cake thingy-ma-bobber and give spray the decorated side with the primer until it's pretty much solid white. Give it about 20 minutes to dry then spray it orange. Let that dry for about an hour.

Step 7: How Long Have We Been at This Now?

This is by far the most irritating of the steps. Using your hand, lightly dust off any loose crispies. Now go out and spray and lacquer the entire cake again. Some of the rice crispies will once again probably fall off. Now go out and spray and lacquer the entire cake again. Once the cake is dry, pick it up and inspect it by turning it around in your hands. Two things will probably happen. One, some more rice crispies will fall off. Two, you will notice some areas that are still white because they didn't get painted. So go out and spray and lacquer the entire cake again. Like I said, this step is extremely frustrating.

Step 8: A Cherry on Top

Once you're done with the previous step, give the cake one last coat of spray paint and lacquer because hey, it never hurts. Now use a screw driver to poke a hole through the middle of the cake, just enough so you can fit your candle in. If you thought you were done spray painting, you were wrong. Go spray and lacquer the top of the cake again just so the cake on the inside of the hole is sealed.
Once that's dry put the candle in and let it burn a little just so it looks good. Now measure around your cake to symmetrically place 8 of your fake cherries on top of your cake. What I did was I put a small blob of caulk where I wanted the cherry and stuck it on. After that I went around the base of each cherry with the caulk gun and made it look more like the actual Portal Cake.

Step 9: This Is a Triumph!

Now your done! I use my cake as a center piece or on my island countertop for decoration. If you actually made it through this instructable, huge congratulations and please post a picture of your finished product.