Preheat oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease lightly.
Toast the walnuts – Spread walnuts on a baking sheet and toast for 5–7 minutes until fragrant. Set aside to cool, then roughly chop.
Mix the dry ingredients – In a medium bowl, whisk together sprouted wheat flour, baking powder, baking soda, and salt.
Mix the wet ingredients – In a large bowl, whisk together melted butter, brown sugar, eggs, milk, and vanilla until smooth.
Combine – Add the dry ingredients to the wet and mix gently until just combined. Fold in 1 cup of the chopped walnuts, reserving the rest for topping.
Fill and top – Fill the muffin cups ¾ of the way full. Sprinkle the remaining walnuts over the tops.
Bake – Bake for 18–22 minutes, or until a toothpick inserted into the center comes out with a few crumbs.
Cool – Let muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.