Yields: 18 muffins
Preheat oven to 400 degrees F.
Line 18 muffin cups with paper or foil liners. Spread the pecans in a pie plate and toast in the oven until fragrant and lightly browned; about 8 minutes.
Let cool completely.
In a food processor, combine the pecans with the brown sugar, cinnamon, and 4 tbsp of the butter, and pulse until the pecans are finely ground and the crumb topping resembles wet sand.
In a medium bowl, whisk the flour with the baking soda and salt.
In a large bowl, using a hand mixer beat the remaining 6 tbsp of butter with the granulated sugar at medium speed until fluffy; about 1-2 minutes.
Beat eggs one at a time until incorporated, then beat in the sour cream, vanilla, and 2 tbsp of water. Beat in the dry ingredients.
Spoon half of the batter into the prepared muffin cups and sprinkle with 1/3 of the crumb topping. Top with remaining batter and sprinkle the remaining crumb topping evenly over the batter.
Bake for about 25 minutes, until the tops are browned and a toothpick inserted in the center of a muffin comes out clean.
Transfer the muffins to a rack to cool for 10 minutes.
Serve warm or at room temperature.