Preheat your oven to 350°F (175°C). Lightly grease an 8x8-inch baking dish with cooking spray and set it aside.
In a medium saucepan over low heat, gently melt the butter with half of the sugar-free chocolate chips until smooth. Alternatively, you can melt them in the microwave in 30-second increments.
Once melted, remove from heat and stir in both sugar-free sweeteners and the vanilla extract. Mix well until everything is fully combined and smooth. Let this mixture cool slightly.
In a separate medium mixing bowl, whisk together the lightly beaten eggs and almond flour until well combined and smooth.
Gradually pour the slightly cooled chocolate mixture into the egg and almond flour mixture. Stir thoroughly until all ingredients are perfectly blended into a thick batter.
Gently fold in the remaining sugar-free chocolate chips and, if desired, the chopped walnuts.
Pour the brownie batter evenly into your prepared baking dish, spreading it out with a spatula.
Bake for approximately 25 minutes, or until a toothpick inserted into the center comes out with moist crumbs. Avoid overbaking for the fudgiest texture.
Allow the brownies to cool completely in the pan before slicing and serving. This helps them set and ensures the best fudgy consistency.