Prepare the Pan. Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper, leaving some overhang for easy removal. Lightly grease the parchment paper with cooking spray.
Melt the chocolate and butter. Combine the butter and semi-sweet chocolate chips in a heatproof bowl. Melt the mixture over a double boiler or microwave it in 20-second intervals, stirring between each, until smooth and fully combined. Let the mixture cool slightly before proceeding.
Mix wet ingredients. In a large mixing bowl, combine the melted chocolate mixture with the brown sugar. Beat the mixture using a hand mixer or a stand mixer at medium speed until fully incorporated, about 2–3 minutes. Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract and a pinch of sea salt.
Mix dry ingredients. In a separate bowl, whisk together the flour, cocoa powder, cornstarch, and baking powder.
Combine. Gradually add the dry ingredients to the wet ingredients, mixing at low speed until combined. Stir in the apple cider vinegar and red gel food coloring, adjusting the amount until the desired shade of red is achieved.
Bake the Brownies. Spread the batter evenly into the prepared pan, smoothing the top with a spatula. Bake for 30–35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. Avoid overbaking to keep the brownies fudgy. Remove from the oven and allow the brownies to cool completely in the pan before removing them.
Prepare the Cream Cheese Frosting. Meanwhile, in a large mixing bowl, beat the softened cream cheese, powdered sugar, and pure vanilla extract on low speed until smooth, about 1 minute. In a separate bowl, beat the butter on medium speed until creamy and fluffy. Gradually incorporate the cream cheese mixture into the whipped butter, mixing until fully combined and smooth. Finally, add the heavy cream and gently fold it into the frosting until well incorporated. Transfer the frosting to a piping bag for easy application.
Assemble and Serve. Once the brownies have completely cooled, carefully lift them out of the pan using the parchment paper overhang and transfer them to a serving dish. Pipe or spread the cream cheese frosting evenly over the surface of the brownies using an offset spatula or piping bag. For neat and clean slices, chill the frosted brownies in the fridge for 15-20 minutes before cutting them into squares or rectangles.