• Heat the oven to 350°F. Generously grease and flour a 10-inch fluted cake pan.
  Butter and flour
• Remove 2 tablespoons of the cake mix and set it aside for the streusel topping. Put the remaining cake mix in a mixing bowl. Add the sour cream, melted butter, and eggs. Beat with an electric mixer on medium speed until smooth and well blended.
  4 large eggs | 1 cup sour cream | 6 tbsp melted unsalted butter | 1 (15.25-ounce) box yellow cake mix

Prepare the Streusel

• Combine the reserved 2 tablespoons of the cake mix with the brown sugar, cinnamon, and chopped pecans.
  1/3 cup brown sugar | 2 1/2 tsp ground cinnamon | 1 cup chopped pecans | 2 tbsp reserved cake mix

Assemble and Bake the Cake

• Spoon half of the cake batter into the prepared pan; smooth it, then sprinkle the streusel mixture evenly over the layer.
  
• Top with the remaining cake batter and gently spread to cover. Tap the pan on the counter to release any trapped air.
• Bake the cake until it is set and a skewer inserted into the center of the cake comes out clean, about 45 to 65 minutes. Remove the cake from the oven and let it cool in the pan for 10 minutes.
  
• Carefully invert it onto a rack that is set over a sheet of foil or baking sheet. Let it cool while you make the glaze.
  

Icing

• For the icing, sift the confectioners' sugar into a medium bowl; add 1 1/2 teaspoons of vanilla and 2 tablespoons of milk; mix, adding more milk if too thick to drizzle.
  1 cup confectioners' sugar | 2 tbsp milk | 1 1/2 tsp vanilla extract
• Drizzle the icing over the cooled cake.