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.