You can use any kind of protein, but I think the chocolate peanut butter flavor is a perfect match. Plant protein leads to a runnier filling, but tastes just as good.
Switch up the nut butter for some variations. Smooth, chunky, salted/unsalted, almond, cashew, peanut, the possibilities are endless!
Test out different extracts in the chocolate topping. Mint is excellent, and I plan to try coffee extract with coffee protein powder. Also, test out maple extract!
Adjust the sweetener to your liking. I imagine it would also work well with honey or agave.