Preheat oven to 350 degrees F. In a large, microwave-safe mixing bowl melt butter and chocolate for 2 minutes (stirring every 30 seconds) until smooth.
Add vanilla extract, Truvia, eggs and applesauce and mix until combined. Add collagen, protein powder and flour and mix until combined.
Press batter into an 8x8-inch baking dish lined with parchment paper. Sprinkle chocolate chips on top.
Bake for 25-30 minutes, or until set and an inserted toothpick comes out clean.