First, make the brownies. Preheat the oven to 350F.
Whisk together the chocolate graham crumbs and 1/2 cup sweetened condensed milk until fully incorporated.
Pour into a lined or greased 9x9 cake pan and bake 8-12 minutes, until an inserted toothpick comes out clean.
While the brownies are cooling, prepare the ice cream base.
Whip up your whipping (heavy) cream with a mixer for at least 4 minutes, until soft peaks form.
The cream will go through several stages, from bubbly, to slightly thickened, to rippling, and finally puffy and airy.
Gently stir in the sweetened condensed milk, along with the vanilla extract. You don't want to deflate the cream, so avoid overmixing.
Fold the ice cream base into a glass cake pan (or lined loaf pan) and sprinkle pieces of the brownie mixture into the ice cream, pushing some pieces further into the ice cream with a spatula.
Cover and freeze for 4 hours or overnight.
Serve with whipped cream, chocolate drizzle, sprinkles, cherries, nuts - the sky is the limit!