- In a bowl, with an electric mixer on medium speed, beat butter, granulated sugar, brown sugar, and peanut butter until well blended.
- Beat in eggs and vanilla until smooth, scraping down sides of bowl as needed.
- In another bowl, mix flour, cocoa powder, baking powder, and salt.
- Stir or beat into butter mixture until well incorporated. Stir in chocolate chips & oats.
- Drop dough in rounded 2-tablespoon portions, 3 inches apart, onto buttered or cooking parchment-lined 12- by 15-inch baking sheets.
- With a lightly floured fork, flatten slightly into 2 1/2-inch rounds about 1/2 inch thick.
- Bake in a 350° oven until cookies are golden and tops feel set when lightly pressed, 8-10 minutes (they will feel underdone but will firm up as they cool);
- Let stand 5 minutes on sheets, then, with a wide spatula, transfer cookies to racks to cool.