For the Brownies:

1 stick (8 tablespoons) unsalted butter, at room temperature
1 cup granulated sugar
2 tablespoons cocoa, plus more for pan
2 eggs
1 teaspoon pure vanilla extract
3/4 cup flour
pinch of kosher salt

For the Ice Cream Sandwiches:

1 quart vanilla ice cream, slightly softened
2 pounds chocolate chips
1 teaspoon oil