Preheat the oven to 350 degrees. Butter a quarter sheet pan (a small jelly roll pan), or a 13x9inch pan. Place a sheet of parchment paper in the bottom, spread with butter, and dust with cocoa powder. Set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream together butter, sugar, and 2 tablespoons of cocoa powder. When the mixture is creamy, and all lumps are gone, add in eggs, one at a time, incorporating well after each addition. Add in vanilla.
Melt the chocolate chips with the oil in the microwave in 30 second intervals, until chocolate is smooth. Dip each ice cream sandwich in the chocolate, and let set on a sheet of parchment paper. Wrap in parchment paper and freeze until ready to serve.
For the Brownies:
For the Ice Cream Sandwiches: