How to Make It
Preheat the oven to 400° and 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 tablespoons 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 powder, baking soda and salt. In a large bowl, using a hand mixer, beat the remaining 6 tablespoons of butter with the granulated sugar at medium speed until fluffy, 1 to 2 minutes. Beat in the eggs 1 at a time until incorporated, then beat in the sour cream, vanilla and 2 tablespoons of water. Beat in the dry ingredients.
Spoon half of the batter into the prepared muffin cups and sprinkle with one-third of the crumb topping. Top with the 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.