Smothering ice cream with loads of toppings is one of my favorite parts of making a sundae! This ice cream pie has a unique cookie base that bakes up crunchy on the edges and chewy in the center, cradling ice cream, toppings and homemade butterscotch sauce. The butterscotch sauce is rich and sweet with a touch of salty and perfectly coats the scooped ice cream.
Preheat the oven to 400 degrees F. Set a baking sheet in the center of the oven. Spray the bottom of a standard 9-inch pie pan with cooking spray.
For the cookie base: Combine the butter, brown sugar, coffee if using, vanilla, salt, baking powder and baking soda in the bowl of a stand mixer fitted with the paddle attachment. Blend on low speed until combined then raise to medium speed and beat until fluffy, 2 to 3 minutes. Scrape the bowl and paddle clean and add the egg. Mix on low speed until combined then raise to medium speed for a few seconds. The mixture may look broken but that’s okay. Add the flour and cocoa and mix on low speed until combined. Scrape the bowl as needed. Add the chocolate chips and nuts and mix on low speed until evenly distributed.
Transfer the dough to the prepared pan. Moisten your fingers to press the dough evenly into the pan and up the sides. Smooth out the dough with a spoon if needed.
Set the pie pan on the preheated baking sheet and bake until puffed and the outer 1-inch edge of the crust feels set, 14 to 15 minutes. Cool on a wire rack until barely warm. It’s okay if the center of the cookie sinks as it cools.
For the butterscotch sauce: Melt the butter in a small saucepan over medium heat and cook until foamy and sizzling. Stir in the sugar, cream, salt and 1 teaspoon water, stirring until the sugar is dissolved. Bring to a boil and boil without stirring for 2 minutes. Remove from the heat and stir in the vanilla. If it looks like the butter has separated from the sauce, add a few drops of hot water and stir until smooth. Pour into a heatproof measuring cup and let cool while assembling the pie.
To assemble: Remove the cookie base from the pan if desired. Fill the center of the cookie crust
with scoops of ice cream. Sprinkle with the marshmallows, almonds and chocolate chips and slice. Drizzle butterscotch sauce over each slice and serve (see Cook’s Note). Cover any leftovers with plastic wrap and freeze for up to 1 week.
If the ice cream melts too quickly, place the assembled pie in the freezer for 30 minutes before slicing and serving.