Preheat oven to 350°F (175°C) and line two baking sheets with parchment.
Cream butter, brown sugar, and granulated sugar for chocolate chip dough. Add egg, vanilla, then flour, baking soda, and salt. Fold in chips.
½ cup unsalted butter, ¼ cup brown sugar, ¼ cup granulated sugar, 1 egg, 1 tsp vanilla extract, 1 ¼ cup all-purpose flour, ½ tsp baking soda, ¼ tsp salt, ½ cup chocolate chips
For brownie dough, whisk butter and sugar, add egg, vanilla, cocoa, flour, baking powder, salt, folding chocolate chips optional.
½ cup unsalted butter, ⅔ cup granulated sugar, 1 egg, 1 tsp vanilla extract, ⅓ cup unsweetened cocoa powder, ⅔ cup all-purpose flour, ¼ tsp baking powder, ¼ tsp salt, ½ cup chocolate chips
Form cookies with 1 tbsp of each dough, press, roll into ball, and place on baking sheet.
Bake 10–12 minutes until edges set. Cool on sheet 5 minutes, then transfer to rack.
Notes
Chill dough balls to prevent spreading.
Freeze shaped dough for later baking.
Bake from frozen with a couple of extra minutes.
Store cookies airtight at room temp for 4 days or freeze for 2 months.