These ones look like they were made by a five year old. I am 27, and have no excuse. YMMV.
Step 1: Collect!
Baking powder (if your flour isn't self raising).
(This is actually adapted from a muffin recipe, but for some reason comes out tasting like scones. Savoury works quite well with the amount of chocolate you're going to be putting on these)
White chocolate (2 - 3 decent sized bars should be enough)
Green food colouring
Cooking oil (Can substitute milk - this is to loosen the chocolate and stop it binding if it dries out during melting).
White chocolate buttons.
Various mixing bowls, whisks, spoons, pans etc. as required.
A small muffin tin. I recommend the silicone type shown in this instructable, as it gives the closest to a mushroom shape I've found and they also pop out of it very easiy without any greasing.
Step 2: Melt! Mix!
Now break a medium egg into your mixing bowl, and whisk it up. Add half a cup of melted butter, then a cup of milk, then whisk them all up. Photos above show this in far too much detail.
Step 3: Mix!
2 and 1/2 cups of flour
2 tablespoons of sugar
and 1/2 a teaspoon of salt.
If your flour isn't self raising, add 2 teaspoons of baking powder too.
Now dump in the wet stuff you mixed in the last step too, and mix it all together until it forms delicious, sticky muffin dough.
Step 4: Bake!
If you're using a silicone tray like the one in the pictures, you don't need to grease it or anything, they'll pop right out when they're done. If you're using a metal tin, you'll need to grease it and might want to use paper muffin cases too.
Bake them at gas mark 5 (190Â°C, 375Â°F) for 25 minutes, and they should look like the ones in the third pic below.
Step 5: Melt!
Break up all your chocolate into a microwavable bowl, then blast it for a while on a defrost setting or the lowest power you have available. Keep doing it until it gets a bit melty like in photo #1, then you can stir it up.
Now add your food colouring, and be ready for something ugly to happen: Chocolate is oily, and most food colouring is water based. So, the same as if you're melting it in a steamer and some water gets into it, when you add colouring the chocolate will immediately seem to dry out and stiffen, going powdery and lumpy in places.
You can sort this out by adding a little bit of cooking oil or milk - not too much or it will get really watery and not be able to set.
Keep adding colouring and oil/milk as needed until you get the shade of green you want, and that's your icing ready.
Step 6: Dip!
Next add the white chocolate buttons to create the white spots, but make sure to let the icing set for a while before doing this. If you add the buttons too early, they'll go blobby and melt off the sides, but if you add them too late, they won't stick.