Prepare the cookies: Preheat the oven to 350°F (175°C) and line two 8-inch round cake pans with parchment paper rounds. Grease the exposed sides with butter or nonstick spray. Adding a bit below the parchment helps it adhere. If you only have one cake pan, don’t worry; the batter will stay fresh while the first round bakes.
In a large bowl, melt half the butter in the microwave or in a medium pot on the stove, then stir until fully melted (this helps maintain a lower temperature). Add salt, brown sugar, and milk, whisking until combined. If it’s still warm, let it cool a bit longer to prevent the egg from scrambling or the chips from melting before adding the egg and vanilla, whisking until well mixed. Sprinkle baking powder over the batter and mix thoroughly. Incorporate the flour and half a cup (3 ounces or 85 grams) of chocolate chips, stirring until the flour is fully blended.
Divide the batter evenly between the two pans and smooth the tops. Sprinkle 2 tablespoons of chocolate chips on each round. Bake for approximately 15 minutes, until the cookies are golden at the edges and set but still soft in the center. Move them to a cooling rack for 5 minutes, then remove from the pans, peeling off the parchment. I prefer to place my cookies in the freezer for 10 minutes to ensure they're completely cold before assembling the cake. If your ice cream is very hard in the freezer, transfer it to the fridge during these 10 minutes for easier scooping.
Assemble the cake: Line one of the 8-inch round cake pans with plastic wrap, extending it up the sides in two directions for easy removal. [An 8-inch springform pan can also work but may leak before the ice cream is fully set, so using some plastic wrap inside is advisable.]
Place the first chocolate chip cookie round, top side down, at the bottom of the pan. Spread vanilla ice cream evenly over it using a spatula. Place the second chocolate chip cookie round, top side up, on top, pressing it firmly against the ice cream. Use any overhanging plastic wrap to cover the cookie, although it doesn’t need to be completely covered.
Chill the ice cream sandwich cake for 3 to 6 hours, preferably overnight, until it firms up.
To complete and serve: Take the cake out of the freezer. Run a knife around the edges of the cake pan, then use the plastic wrap to lift the cake out. Pat the remaining 1/2 cup of chocolate chips onto the sides of the cake. Slice the cake into 8 to 12 wedges and serve immediately.
Make ahead: The ice cream cake can be stored in the freezer for weeks, although I’ve never had one last that long.
Note: For individual ice cream sandwiches, use the (Abridged) Blondie Chipwich recipe from Smitten Kitchen Keepers: Pour the batter into a single 9×13-inch pan. After baking, cut the cookie in half, flip each half so the top sides face out, and fill with ice cream, using the pan’s sides to help maintain shape. Once frozen solid again, cut into 12 smaller squares and press reserved chocolate chips onto the sides. For the complete recipe and 99 other amazing ones (that I might be biased about), be sure to check out Smitten Kitchen Keepers wherever cookbooks are sold.
I transformed my beloved ice cream sandwich into a wonderfully simple giant ice cream sandwich cake, and now we’re aware of what our weekend is missing.