Mix brown sugar, butter, and peanut butter in a large bowl with a hand mixer until creamy (about 2 minutes).

Add eggs and vanilla, continue beating until mixed.

Add flour, cocoa, and baking powder and beat on low speed until well mixed.

Divide the dough in half. Place each half on a sheet of plastic wrap and form into a log.

Wrap well and chill until firm, 4 hours or overnight. (This process can be sped up by freezing the dough for 1-2 hours.)

Preheat oven to 350°F. Line two cookie sheet with parchment paper or a silicone baking mat.

Working with one dough log at a time, cut slices 1/4” thick and place 2” apart on baking sheet.

Bake for 8-10 minutes, or just until they loose their glossy sheen. Cool on cookie sheets 10 minutes then remove to a rack to cool completely.

Once cookies are cool, place chocolate chips and oil or shortening in a microwave safe bowl.

Heat on 50% power for about 2-3 minutes, stirring every 30 seconds, or until chocolate is melted and smooth.

You can dip each cookie in the chocolate then dip in the toppings. Or, for a more decorative approach, place the melted chocolate in a sandwich bag and cut off one tip. Drizzle chocolate over cookies and sprinkle with toppings.