Preheat oven to 350°F. Line two (18×13-inch) rimmed baking sheets with foil and spray generously with non-stick cooking spray. Set aside.
In a large microwavable bowl, melt the butter and chocolate chips, stirring every 30 seconds, until melted and smooth. Let cool slightly. Whisk in the sugar then the eggs and vanilla until well combined.
In a medium bowl, whisk together the flour, cocoa, baking soda and salt. Add to the chocolate mixture, stirring until thick and smooth.
Divide the dough in half and press each half into the bottom of the prepared baking sheets. The dough should be thin and cover the bottom of the pan completely.
Bake for 10 minutes, rotating the sheets half way through. Let the baking sheets cool on a wire rack for 15 minutes and then put them in the freezer for an additional 15 minutes.
Meanwhile, beat the ice cream on low speed in an electric mixer fitted with the paddle attachment until smooth. Stir in the chocolate chips.
Once the cookie sheets have frozen for 15 minutes, remove and spread one cookie completely and evenly with the ice cream. Lift the other cookie from the pan with the sides of the foil. Flip the cookie over onto the ice cream layer of the other cookie sheet and press down gently. Remove the foil from the cookie that is now the top layer. Tent the cookie sheet with another piece of foil and return to the freezer for at least 2 hours.
To cut the ice cream sandwiches, lift them from the cookie sheet with the foil and place on a flat work surface. With a sharp knife, cut into rectangles measuring about 2.25 x 4-inches in size. You should get 21 ice cream sandwiches total.
Serve immediately or wrap each sandwich tightly with plastic wrap and return to the freezer until ready to serve.
