Preheat oven to 350°F. Grease two 8x8-inch square pans and line bottoms with parchment paper, leaving 4-6 inches of overhang on two sides.
In a large bowl, mix melted butter, granulated sugar, and brown sugar with a hand mixer on medium speed until smooth and glossy, about 2 minutes.
Add eggs one at a time, mixing well after each addition. Mix in oil and vanilla extract.
In a separate bowl, whisk together flour, cocoa powder, and salt. Gradually add dry ingredients to wet mixture on low speed until just combined.
Divide batter evenly between prepared pans and spread into corners. Bake for 30-40 minutes until toothpick inserted in center comes out with few moist crumbs.
Cool brownies in pans for 10 minutes, then lift out using parchment overhang. Remove parchment from one brownie only. Cool completely to room temperature.
Let ice cream soften at room temperature for 5-10 minutes. Place brownie with parchment back in pan and spread ice cream evenly over top.
Invert second brownie (parchment-side up) onto ice cream layer, pressing gently. Cover tightly and freeze for at least 6 hours or overnight.
Remove from freezer and let sit 5-10 minutes. Lift out using parchment and cut into 8 squares with sharp knife. Serve immediately.