0.5cupunsalted butter, softened to room temperature
0.5cupsour cream
3largeeggs, at room temperature
1teaspoonvanilla extract
1teaspoonbaking powder
0.5teaspoonbaking soda
0.5teaspoonsalt
1tablespoonground cinnamon
0.5cuppacked brown sugar, light or dark
0.5cupchopped walnuts or pecans (optional)
Instructions
Preheat the oven to 350°F (175°C). Prepare a 9x13-inch baking pan by greasing it with butter and lightly dusting it with flour.
In a large mixing bowl, cream together the softened butter and granulated sugar using an electric mixer on medium speed until light and fluffy, about 3-4 minutes.
Add the eggs one at a time to the butter-sugar mixture, mixing on low speed after each addition until fully incorporated. Stir in the vanilla extract until evenly blended.
In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. Gradually add this dry mixture to the wet ingredients, alternating with the sour cream, beginning and ending with the flour mixture, mixing just until combined.
In a small bowl, combine the packed brown sugar, ground cinnamon, and chopped nuts (if using) to create the streusel topping.
Pour half of the cake batter into the prepared baking pan, spreading it out evenly. Sprinkle half of the streusel mixture over this layer of batter.
Carefully pour the remaining cake batter on top, smoothing it out gently. Sprinkle the rest of the streusel topping evenly over the surface.
Use a knife or toothpick to gently swirl the streusel topping into the batter to create a marbled effect, being careful not to mix it in completely.
Place the pan in the preheated oven and bake for 35-40 minutes, checking for doneness with a toothpick inserted into the center of the cake.
Allow the coffee cake to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely before slicing.
Notes
For an elegant finish, serve the coffee cake warm or at room temperature, lightly dusted with powdered sugar.