Preheat the oven to 350°F (175°C). Line a muffin pan with paper liners.
In a small saucepan, cook the butter over medium heat until it bubbles and the milk solids brown at the bottom. This takes about 5 minutes. It should smell nutty. Remove from heat and transfer to a bowl to cool.
In a large mixing bowl, whisk together the gluten-free flour, hazelnut flour, tapioca starch, baking powder, salt, cinnamon, ginger, nutmeg, and cardamom.
In a separate bowl, whisk the eggs, maple syrup, brown sugar, vanilla bean seeds, and cooled brown butter until well combined.
Add the wet mixture to the dry ingredients and stir until just combined.
Fold in the grated apples evenly.
Scoop the batter into the prepared muffin liners, filling each about 3/4 full. Garnish with chopped pistachios and/or apple slices on top.
Bake for 20–25 minutes, or until a toothpick inserted in the center comes out clean.
Transfer muffins to a wire rack and let them cool completely before serving.