Make the crust: Place cereal in a food processor and pulse until you have fine crumbs. Alternatively, you can crush the cereal in a Ziploc bag with a rolling pin (or your hands). Add the melted butter and process (or stir) until combined. The texture should be similar to wet sand.
Build the cake: Press half of the ground cereal-butter mixture into the bottom of an 8-inch springform pan. Spread half of the softened ice cream on top of the crust. Pour dulce de leche on top of the ice cream and carefully spread. Sprinkle the remaining crust on top of the dulce de leche and carefully press down on it with your hands.
Spread the remaining softened ice cream on top of the second cinnamon toast crunch crust layer. Cover with plastic wrap and freeze until frozen, 6 hours or up to overnight.
When ready to serve, carefully cut around the pan with a knife to loosen the cake from the springform sides. Remove the springform sides. Take off the plastic wrap and drizzle the top of the cake with dulce de leche. Decorate with more Cinnamon Toast Crunch.