Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking pan.
Mix melted butter spread, sweetener, cocoa powder, vanilla extract, eggs, flour, baking powder, and salt together in a large bowl. Pour into the prepared pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 20 minutes.
