I think the real key to these is not to prank the whole batch. One or two, sprinkled throughout, gives the desired effect with an added bonus: Since people will have had a few regular cookies, they won't expect the next one to be bad. It puts their guard down, as it were. However, if you plan on partaking of the good cookies, be sure to remember which ones are pranked, and save yourself from a major backfire.
These are super easy to make. Though if you bring them to a party, be aware suspicion will be tagged onto your food for a while afterwards.
And these are by no way only April Fools Day treats... or maybe only someone with my dry sense of humor thinks so? It's up to you to decide.
Step 1: Supplies
*Sugar Cookies, or any other frostable cookie. Soft ones are better because they are easier to cut into
*Frosting - Any type will do
*Some not so yummy cookie fillers - I used a mix of pepper, chili powder, and salt. But anything will work
Step 2: Cutting the Cookie
Take your cookie and a sharp knife, and slowly chip away at the center. You don't want to break through the back, and you also don't want to get to close to the side, so go as low as you can without puncturing and keep around a quarter inch of boarder. (With more edge, you won't have to take the frosting all the way to the tip, so it will look more like a normal cookie and less of a mess to handle. It will probably also be more stable) I think a sharp angle into the indentation works better than a shallow one, because it holds the spices better. But that's just a theory.
There's really no rhyme or reason to removing the center, just do it carefully and slowly whichever way you can.
Step 3: Fill Your Cookie
Step 4: Frost Your Cookie
No way to make a piping bag? There is an alternative method. Mix your seasonings in with just a little frosting, so they get nice and sticky. Smooth it over the hollow center, making sure not to get any on the edge. Then it should be easier to take a knife and carefully add a regular frosting layer over the top.
(Can you tell which cookie is the bad one in the third picture?)