Preheat the oven to 400F. Line a baking sheet with parchment paper. Spread the walnuts out on the baking sheet in a single layer. Bake for 7 to 8 minutes until golden brown and fragrant. Remove them from the oven and let them cool.

In a large mixing bowl, sift together the flour, baking powder, cinnamon, nutmeg and salt.

In a medium sized bowl, beat the brown sugar and butter together. Then, beat in the eggs, maple syrup, milk, maple extract and vanilla extract together until well combined.

In two parts, add the wet ingredients to the dry ingredients, alternating with the milk. Mix only until combined. Fold in 1 cup of the toasted walnuts.

Line a 12 muffin tin with muffin liners. Divide the batter evenly between 12 muffin liners.

In a small bowl, mix the flour, brown sugar, white sugar, butter, toasted walnuts, cinnamon and hazelnut extract together. The mixture should be clumpy. Sprinkle the streusel topping evenly on top of each muffin.

Bake the muffins at 400F for 5 minutes. Then, decrease the oven temperature to 375F without opening the door. Continue to bake for another 16 to 17 minutes until a toothpick inserted comes out clean.

While the muffins are baking, mix together the icing sugar, milk, maple syrup and maple extract until smooth. Once the muffins are done baking, let them cool completely to room temperature. Then, drizzle the maple glaze over top of each muffin. Let sit for a few minutes to solidify.