Step 1

Prepare streusel topping: In a medium bowl, stir together brown sugar, flour, and salt. With a pastry blender or two knives, cut in butter until mixture resembles large coarse crumbs; refrigerate until ready to use.

Step 2

Preheat oven to 350 degrees. Prepare muffins: Butter and flour a jumbo 12-cup muffin tin (or two 6-cup muffin tins). In a small bowl, whisk together flour, baking powder, and baking soda; set aside.

Step 3

Using an electric mixer on medium speed, beat together butter, sour cream, granulated sugar, and vanilla until light and fluffy. Beat in eggs, one at a time, until well combined. With mixer on low, beat flour mixture into butter mixture.

Step 4

Divide half the batter among prepared muffin cups. Top with half the streusel mixture, then remaining batter, and top with streusel. Bake 25 to 30 minutes or until a toothpick inserted in center of a muffin comes out clean. Cool in pan 5 minutes, then transfer to a wire rack to cool completely. Dust with confectioners' sugar, if desired.