Step 1

Preheat the oven to 350°F. Grease a 13x18-inch sheet pan and line the bottom with parchment paper.

Step 2

Make the brownies: In a large saucepan, warm the butter, chocolate chips, and oil over medium heat. Stir slowly until melted and smooth, then remove from heat and set aside to cool slightly.

Step 3

In a large bowl, beat the eggs, sugars, vanilla, and salt on medium-high speed until thick and pale. Gently stir the chocolate mixture in by hand with a spatula, followed by the flour, cocoa powder, and mini chocolate chips, if using.

Step 4

Pour the batter into the prepared sheet pan, spreading it evenly. Bake for 20-25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. Be careful not to overbake.

Step 5

Make the frosting: In a medium saucepan, warm the butter, milk, and cocoa powder over medium heat. Stir until smooth, then remove from heat and carefully whisk in the powdered sugar and vanilla extract. Whisk until smooth and spreadable.

Step 6

Let the brownies cool in the pan for about 10 minutes before spreading the warm frosting evenly over the top. If desired, sprinkle coarsely chopped walnuts or extra mini chocolate chips on top.

Step 7

Let the frosted brownies cool completely before cutting them into squares or bars. Enjoy your rich, fudgy Texas Sheet Cake Brownies—a perfect treat for any occasion!