Mix brownie batter:

Mix the brownie mix with eggs, oil, and water (or milk if the box says so) following the package instructions. Use the quantities listed on the box if they differ from those here.

Line muffin tins:

Place paper liners in muffin tins (without liners, brownies will stick; if omitting liners, coat cups thoroughly with nonstick spray).

Fill muffin cups:

Divide brownie batter among 18 muffin cups, filling each about half full or a bit less.

Top with cookie patties:

Shape the cookie dough into small patties that are narrower than the muffin cups, then set one on top of each brownie portion so that it rests with some batter visible around its edge.

Bake brookies:

Bake at 350°F (175°C) for 20–22 minutes, until a toothpick inserted comes out with moist crumbs attached.

Release from pan:

If you skipped paper liners, allow the brookies to cool for roughly 10 minutes, then slide a plastic knife around each one to release it from the pan.