Either the night before or in the morning, make the filling.
Beat the heavy whipping cream until it starts to form soft peaks.
Add the ice cream a 1/2 cup at a time, beating until it becomes incorporated into the whipped cream.
Pour into standard-sized muffin tins and put in the freezer for the whole day or overnight.
Once they've set overnight, take them out of the freezer. Place parchment paper on a baking sheet. Run a knife along the edge of each muffin hole and pry out the ice cream fillings, placing them on the parchment paper. Put them back in the freezer.
Preheat the oven to 350 degrees Fahrenheit.
Melt the butter in the microwave.
Beat the butter and sugars together until smooth and creamy.
Add the vanilla extract and egg and beat on low until just incorporated (about 12 seconds).
Beat in the flour, baking soda, and salt until they are fully incorporated.
Add the chocolate chips and the chopped chocolate chunks and mix into the dough with a spatula.
Roll the dough into 13 or 14 balls and place them on a baking sheet lined with parchment paper or a non-stick baking mat.
Bake for 10 to 13 minutes until slightly darker around the edges.
Let the cookies cool on the pan and then transfer them to cooling racks.
Once the cookies are completely cool, grate about 1/4 cup bittersweet chocolate onto a plate. Add 1/4 cup sprinkles on top and shift the plate a little to mix them together.
Take one of the ice cream filling servings out of the freezer and quickly roll the edges in the grated chocolate and sprinkles. Place it on top of one cookie and then take another cookie and place on top. Serve immediately. If you want to serve the ice cream sandwiches all at once just place each finished ice cream sandwich in the freezer while you assemble the others.
Notes
12 balls of dough make cookies a little too big for the ice cream fillings so 13 or 14 works best, but it's slightly different every time.