Preheat the oven to 350 degrees F or 175 degrees C
Line a standard muffin tin with 12 paper liners.
For the Streusel Topping:
In a small bowl stir the brown sugar, cinnamon and Bisquick together.
Using a pastry cutter or a pair of knives cut the butter into the dry mixture until the butter looks like large crumbs then mix in the chopped walnuts and set the bowl aside in the refrigerator.
For the Muffin Batter:
In a large mixing bowl whisk together the eggs, mashed sweet potato, brown sugar, melted butter, milk, cinnamon, and nutmeg until everything is thoroughly combined.
Using a rubber spatula, stir the gluten free Bisquick into the wet ingredients until the wet and dry ingredients are thoroughly incorporated but don’t over mix.
Evenly divide the batter between the 12 paper liners.
Spoon heaping tablespoons of the streusel mixture over the tops of each muffin.
Bake at 350 degrees F or 175 degrees C for 20 to 24 minutes, or until a toothpick inserted comes out clean.