The way i make them is with 2 boxes of mix, so you need a whole cup of bud butter. A 1/4-1/2 is good, anything less would be pointless, anything more wont absorb into the butter.

as far as penut butter goes, you could put spoon fulls on top before you bake it. or when it's just done, put like chocolate bars on top and let the heat of the brownies melt them.
here is my personal fav recipe
Moon brownies
2 boxes of brownie mix
1 whole package of butter..... highest fat content possable.
1/4-1/2 of the finest cheaba
800mg of 5-htp or about 16-18 capsuls broke open. (optional)
chocolate chips or candy bars. somthing to put on top....mmmmmmm
a big baking pan.

Brake up the tree as fine as possable, hand grinders work nice. Melt down the butter on low, then add the tree and raise the heat. You want the butter simmer not boil. Stir for about 20-30 min, and strain out the plant mat. Your looking for 1-cup of melted cannabutter.

fallow the directions on the box, using the melted butter instead of oil. Also add in the 5-htp, mix it up and bake. The box says for 1 box bake for 20-30 min,use the same baking temp just add like 15 min to the time. Then start checking it with a toothpick. right when it's done, kill the oven, and sprinkle your goodies on top. Chocolate chips, candy bar pieces, penut butter, put it back in the over for 2 min just to melt them. let cool and enjoy. Eat 2 wait 45-1hour. then you should be on the moon.