Preheat oven to 350°F (175°C). Grease and flour a 9x5 inch loaf pan. Line with parchment paper, leaving an overhang on the long sides.

In a small skillet, melt 1 tablespoon butter over medium heat. Add chopped pecans and cook, stirring frequently, until lightly toasted and fragrant, about 3-5 minutes. Remove from heat and set aside.

In a medium bowl, whisk together almond flour, coconut flour, whey protein powder, baking powder, and salt. Set aside.

In a large bowl, cream together the softened 1/2 cup butter and brown sugar replacement until light and fluffy. Beat in the eggs one at a time, mixing well after each addition.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Fold in the toasted pecans.

Pour the batter into the prepared loaf pan and smooth the top. Bake for 50-60 minutes, or until a wooden skewer inserted into the center comes out clean. If the top browns too quickly, loosely tent with foil.

Let the cake cool in the pan for 15 minutes before inverting onto a wire rack to cool completely. Slice and serve.