Spiked Grasshopper Milkshake

Preheat oven to 350°. Whisk flour, chocolate chips, cocoa powder, salt, and baking powder in a medium bowl. Using an electric mixer on medium speed, beat butter, sugar, and vanilla in a large bowl until light and fluffy, about 4 minutes. Reduce speed to low and mix in dry ingredients until just incorporated, about 1 minute. Transfer dough to a large piece of plastic wrap and shape into a 1–1¼" thick log. Wrap tightly; chill until firm, 1–1 ½ hours.

Slice dough crosswise into ¼–⅓" thick rounds and arrange on a parchment-lined baking sheet, spacing ½–1" apart. Bake, rotating baking sheets halfway through, until tops and sides are firm and dry to the touch, 16–20 minutes. Let cool.

Do Ahead: Cookies can be baked 3 days ahead. Store airtight at room temperature.

Purée ice cream, milk, and both liqueurs in a blender until smooth. Transfer to a small bowl or airtight container; cover and freeze until shake has returned to a thick consistency, about 2 hours.

Coarsely crush 5 or 6 cookies (you should have about ½ cup) and stir into shake. Serve in chilled glasses.

Do Ahead: Shake can be made 4 hours ahead. Keep frozen, stirring occasionally and removing from freezer if needed to keep it from freezing solid.