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.