Mix brownie mix, eggs, oil, and water until no dry pockets remain.

Spread in a parchment-lined 9-by-13-inch pan. Bake at 350°F for 22 to 25 minutes until center reaches 160°F and a tester has moist crumbs.

Cool completely; chill 30 minutes. Cut into 16 equal rectangles.

Spread 3/8 cup softened ice cream on eight brownie rectangles.

Top with remaining brownies and a small pinch of flaky salt.

Freeze 1 hour until firm; serve straight from freezer.