Makes 12 muffins
For the Streusel:
For the Muffins:
First make the streusel; on a baking sheet spread out the chopped pecans in an even layer. Bake until toasted and fragrant, about 5 minutes. Remove the nuts and let them cool. In a medium bowl, add the cooled pecans, dark brown sugar, cinnamon, salt and melted butter. Make sure to incorporate all of the brown sugar to break up any lumps. It's going to smell delicious.
Line a standard 12-hole muffin tin with paper liners.
In the bowl of an electric mixer, beat the butter, lemon zest and sugar with the paddle attachment on medium speed for 5 minutes until it's fluffy. Add the egg, then the sour cream and vanilla extract, waiting for each new ingredient to incorporate into the batter. In a medium bowl, sift together the flour, baking powder and salt. With the mixer on low, slowly add the flour mixture until just combined. The batter is going to be thick-ish, almost like dense cake batter.
Scoop the batter into each muffin cup, filling up about 1/3 full (about a tablespoon's worth). Then, sprinkle 1 tablespoon of the streusel on top of each muffin. Or more. We won't tell. Evenly distribute the remaining batter between the 12 muffin cups. Each cup will be fairly full. Sprinkle the remaining streusel over each of the muffins. We pushed it down into the batter a little bit so that we could pile as much streusel on top of each muffin cup without totally over-flowing them.
Bake for 25 minutes, rotating halfway through to ensure even cooking.
Transfer the tin to a cooling rack for 10 minutes. Turn the muffins onto the rack to cool further. Serve warm or at room temperature.