If you make butter first, then add to the goodies, just make the butter, then make your best guess about a serving, and give that to your friend on a cracker or toast or something and ask them if it's the right strength, then go from there.
If the friend normally only smokes, they may not even know how many MG they want in an edible, so a tester is probably the best way to know.
Then when you find the right dosage, just times by 12, and add that amount to a batch of goodies, and cut into 12 pieces.
Rolo pretzel turtles for me.
Lay out some mini pretzel twists on a baking sheet with parchment paper and top each with a Rolo candy.
Put in a low oven for maybe 6-10 minutes, until the Rolos are soft but not melted.
Then quickly press a pecan on top of each one right when they come out, then let cool.
I've also done it with animal crackers and almonds.