01 -
Preheat your oven to 350℉/175℃. Grease an 8-inch cake pan generously with butter.
02 -
In a small bowl, whisk together 2 tablespoons light brown sugar, 1 tablespoon all-purpose flour, and 1 teaspoon cinnamon. Set aside.
03 -
In a medium bowl, combine ½ cup light brown sugar, ¾ cup all-purpose flour, 1 teaspoon cinnamon, ⅛ teaspoon salt, and ½ cup chopped pecans or walnuts if using. Add ½ cup cold unsalted butter (cubed) and mix with your fingers until crumbs form and butter is evenly distributed. Set aside.
04 -
In a large bowl or stand mixer, cream together ½ cup unsalted butter with 1 cup granulated sugar on medium-high speed until pale and fluffy, about 3-5 minutes. Add 2 large eggs and mix until incorporated. Add 1 cup sour cream and ½ teaspoon vanilla extract, mixing until well combined.
05 -
In a separate bowl, whisk or sift 1½ cups all-purpose flour with ½ teaspoon baking powder, ¼ teaspoon baking soda, and ¼ teaspoon iodized salt.
06 -
Add the dry ingredients to the creamed butter mixture and fold gently with a spatula or wooden spoon until just combined.
07 -
Spoon half of the batter into the prepared pan and smooth into an even layer. Sprinkle the cinnamon filling evenly over the batter.
08 -
Spoon the remaining batter in dollops evenly over the filling and smooth into an even layer. Sprinkle the streusel mixture evenly over the top of the batter.
09 -
Bake the coffee cake in the preheated oven for 35-45 minutes or until a toothpick inserted in the center comes out clean or with a few crumbs. Check after 25 minutes; if the streusel is browning too much, lightly tent with foil and continue baking.
10 -
Remove the cake from the oven and let cool for at least 10 minutes before serving.