Brownie Slabs:

Line two 8 x 8-inch square tins with parchment, allowing a 1-inch overhang on all sides. Spray generously with nonstick spray.

Preheat oven to temperature specified on package.

Prepare brownie batter according to package directions. Stir in 140 grams crushed Oreos, and half of the miniature chocolate chips.

With a kitchen scale, weigh batter evenly between the two tins. (Each portion should weigh about 475-500 grams.) Scatter additional crushed Oreos and remaining miniature chocolate chips over one portion.

Bake in preheated oven for about 30 minutes, or until set. Sit tins on a wire rack and allow to cool completely, about 4 hours.

Assembly:

Line a quarter-sheet tray with parchment, wax paper, or a silicone mat. Remove ice cream from freezer and allow it to soften at room temperature until it reaches the consistency of very soft soft serve, about 30 minutes.

Lifting by the parchment overhang, remove the plain brownie slab from the tin. Place it upside down on prepared tray. Peel away parchment.

With a flexible rubber spatula or small stepped palette knife, spread softened ice cream over the slab.

Freeze on tray for 1 1/2 to 2 hours, or until ice cream is very firm, but not rock solid.

Place the decorated brownie slab, Oreo side-up, on top of the ice cream. With your fingertips, press down gently to secure.

Tightly cover tray with foil or plastic wrap. Freeze until brownies and ice cream are both very solid, at least 12 hours, or overnight.

With a sharp chef’s knife, trim edges.

Slice slab into 8 portions, running knife under hot water after every cut.

Serve immediately, or return to freezer until ready to serve.

Store ice cream sandwiches in the refrigerator for up to 2 weeks.