Preheat the oven to 350°F and line an 8.5x4.5-inch loaf pan with parchment paper.
In a large bowl, whisk together the almond flour, coconut flour, baking powder, salt and garlic powder.
In a separate bowl, whisk the eggs, sour cream and melted butter until smooth. Stir the wet mixture into the dry ingredients, then fold in the mozzarella and 1/4 cup of the parmesan. The batter will be thick.
Spread half of the batter into the pan and dollop half of the pesto over it. Add the remaining batter, dollop the rest of the pesto on top and swirl through both layers with a skewer in a figure eight pattern.
Sprinkle with the remaining parmesan and the pine nuts. Bake for 45 to 50 minutes, tenting with foil after 25 minutes, until golden and a toothpick comes out clean.
Cool in the pan for 15 minutes, then transfer to a rack. Slice once cooled and enjoy it toasted, with soup or as the ultimate grilled cheese bread.