Preheat oven to 350 degrees. Line two 9 x 9 inch square pans with parchment, leaving some to overhang the sides.
In a microwave-safe bowl, melt the butter and chocolate chips for 1 minute. Stir until the bowl is no longer warm. If needed, heat 20-30 seconds longer until the mixture is very smooth. Whisk in the sugar and brown sugar.
In a separate bowl, beat the eggs until very frothy and bubbly, about 3-4 minutes. Lower the speed and stream in the chocolate mixture. Whip in the instant coffee (if using) and vanilla.
Add the flour, cocoa powder, baking powder, and salt. Stir until just combined.
Divide the brownie batter between the two pans, spreading it from edge to edge. It will be thick!
Bake for 20-25 minutes until the center is set and an inserted toothpick emerges with just a few moist crumbs. Place the pan on a wire rack and let cool completely. If you have the time, I highly recommend refrigerating the brownies, in the pans, overnight to firm them up and make them even fudgier.
Set the ice cream on the counter for 10-15 minutes until very thawed and easily scooped.
Pull one of the brownie layers out of the pan and invert so the shiny, crinkly top is facing the bottom. Set back onto the parchment and return to the pan. Scoop the ice cream onto this layer, spreading evenly. Remove the second brownie layer from the parchment and press on top of the ice cream. Cover and freeze at least 6 hours, but preferably overnight.
Use a sharp sharp knife to carefully slice the brownies into 12 bars. Freeze again if needed for about an hour to firm up. Enjoy!