Combine milk and chocolate chip cookies in a bowl. Stir and steep for 20–25 minutes.

Strain through a fine mesh sieve, pressing gently to extract all the flavor.

Measure 1 cup for the cake and reserve the rest to drizzle over layers.

Preheat oven to 325°F. Grease and flour three 6-inch cake pans and line with parchment.

Whisk flour, baking powder, and salt in a bowl.

Cream butter and both sugars until pale and fluffy (about 3 minutes).

Add eggs one at a time, mixing fully after each. Add vanilla.

Alternate adding flour mixture and cookie milk, beginning and ending with flour.

Fold in mini chocolate chips gently.

Bake 35–40 minutes or until a toothpick comes out mostly clean.

Cool in pans for 10 minutes, then transfer to a wire rack to cool completely.

Whisk egg whites and sugar in a mixer bowl.

Place over a double boiler and whisk constantly until smooth and no longer grainy (about 3 minutes).

Whisk on medium-high until stiff peaks form and bowl cools.

Switch to paddle and slowly add butter until smooth.

Add vanilla and mix until silky.

Combine chopped chocolate and cream in a microwave-safe bowl.

Microwave in short intervals, stirring between each, until smooth and glossy.

Cool slightly before using.

Level cake layers if needed.

Drizzle reserved cookie milk lightly over each layer.

Frost with vanilla buttercream between layers and around the cake.

Pour ganache over the top for a drip effect.

Decorate with extra cookies if desired.