Using a large bowl and an electric mixer, add heavy cream and whip until soft peaks form. Add cocoa powder, espresso powder, vanilla extract and condensed milk; stir lightly until well combined.
Continue whipping until stiff peaks form. Carefully fold in chopped chocolate.
Transfer mixture into freezer-safe container and press wax paper to top of surface. Freeze for at least 6 hours, or overnight.
For the Brownies
Preheat oven to 350°F.
Line an 8” square baking pan with parchment paper, allowing 2” of overhang on all sides. Set pan aside.
Using a medium saucepan, add the butter, unsweetened chocolate and 1 cup of chocolate chips. Place over medium-low heat, stirring often, until butter and chocolate have fully melted; set pan aside to cool.
In a large bowl, mix together the eggs, sugar and vanilla. Stir the egg mixture into the warm (not hot!) chocolate mixture.
In a medium bowl, sift together the flour, baking powder and salt. Stir the flour mixture into the chocolate mixture.
Stir the remaining ¾ cup of chocolate chips into the batter.
Transfer batter into prepared baking pan. Bake at 350°F for 35-40 minutes, or until a toothpick inserted into brownies comes out mostly clean.
Let entire pan cool completely. (Tip: If you refrigerate these brownies, they’ll be easier to slice.)
Using the parchment paper, life the entire (unsliced) brownie from pan and place on large cutting board. Use a serrated knife to slice the brownie in half horizontally. Place the base of the brownie back into the baking pan. (Tip: Reuse the parchment paper as it will make it easier to remove bars from pan later.)
Spread the ice cream evenly over brownie base. (Tip: If necessary, let the ice cream soften a bit until it is spreadable.)
Place the top of the brownie on top of ice cream and press lightly. Cover pan tightly with plastic wrap and freeze for 4 hours, or overnight.
Lift the bars from the pan and cut into squares. Serve immediately.