1. Line a 9×13-inch pan with parchment paper or foil, leaving an overhang on the sides to help lift the ice cream cake out later.

2. Crush 24 Oreo cookies into fine crumbs, then stir them together with the melted butter until the mixture is evenly moistened. Press the crumbs firmly into the bottom of the prepared pan to form a compact crust.

3. Let the vanilla ice cream sit at room temperature for 10–15 minutes, or until it’s soft enough to spread but not melted. Scoop the softened ice cream over the Oreo crust and gently smooth it into an even layer with an offset spatula.

4. Place the pan in the freezer for 30–45 minutes, or until the ice cream layer is fairly firm and can support the next layers without sinking.

5. Warm the chocolate fudge sauce just until it’s pourable but not hot, then carefully spread it over the chilled ice cream in an even layer from edge to edge.

6. Scatter half of the roughly chopped Oreos over the fudge layer, pressing them lightly so they settle into the sauce and create a crunchy, chocolaty ribbon through the middle of the cake.

7. Spoon the whipped topping over the cookie and fudge layer and spread it into a smooth, fluffy blanket that completely covers the surface of the cake.

8. Sprinkle the remaining chopped Oreos and the sprinkles or mini chocolate chips over the top, gently pressing them into the whipped topping so they adhere.

9. Return the pan to the freezer and chill the cake for at least 4 hours, or until completely firm; freezing overnight gives the neatest slices.

10. When you’re ready to serve, use the parchment or foil overhang to lift the cake out of the pan, let it sit at room temperature for 5–10 minutes to soften slightly, then slice into squares and drizzle each piece with chocolate syrup if desired.