01 -
Preheat the oven to 325°F. Line an 8 by 8-inch metal pan with parchment paper, leaving an overhang.
02 -
In a large microwave-safe bowl, add the butter. Microwave for about 1 minute, or until the butter is melted. Whisk in the granulated sugar and light brown sugar, then let cool to just warm.
03 -
Whisk in the eggs, egg yolk, and vanilla. Whisk vigorously for 30 seconds. Whisk in the vegetable oil and cocoa powder until smooth.
04 -
Using a rubber spatula, stir in the all-purpose flour, cornstarch, and sea salt until combined. Stir in the chocolate chips and toffee bits, reserving a handful of each.
05 -
Spread the brownie batter evenly into the prepared pan. Sprinkle with the reserved toffee bits and chocolate chips.
06 -
Place in the oven and bake for 30 minutes, or until the brownies are set and a cake tester inserted into the center has moist crumbs attached. For less fudgy brownies, bake an additional 5-7 minutes, or until only melted chocolate attaches to the tester.
07 -
Let the brownies cool completely before cutting and serving. Store in an airtight container at room temperature for up to 3 days or up to 5 days in the fridge.