Preheat the oven to 350°F (180°C).
Place 1 cup butter in a large microwave-safe bowl and heat until melted; alternatively melt the butter on the stovetop.
Stir 7 tablespoons cocoa powder into the melted butter until smooth and well combined.
In a separate small bowl, beat 4 eggs until well combined, then stir in 2 1/2 cups monkfruit sweetener until evenly mixed.
Pour the egg–sweetener mixture into the butter–cocoa mixture and stir to combine.
Add 1 1/3 cups white whole wheat flour, a pinch of salt, and 2 teaspoons vanilla; stir until just combined and no dry streaks remain.
Use your fingers to break walnuts into pieces until you have 1 cup, then gently fold them into the batter.
Spray an 8×11-inch (or similar) glass baking dish with nonstick spray. Spread the batter into the dish and smooth the top so it is even.
Bake in the preheated oven for 30 minutes, or until a toothpick inserted near the center comes out with a few moist crumbs.
Let the brownies cool in the pan for 10–15 minutes before cutting into squares.