Sour Cream Coffee Cake With Brown Sugar–Pecan Streusel

1. FOR THE STREUSEL: Process flour, granulated sugar, 1⁄4 cup brown sugar, and cinnamon in food processor until combined, about 15 seconds. Transfer 1-1⁄4 cups of flour-sugar mixture to small bowl and stir in remaining 1⁄4 cup brown sugar; set aside for streusel filling. Add butter and pecans to mixture in food processor and pulse until nuts and butter resemble small pebbly pieces, about 10 pulses. Set aside for streusel topping.
2. FOR THE CAKE: Adjust oven rack to lowest position and heat oven to 350 degrees. Grease and flour 10-inch tube pan softened butter. Whisk eggs, 1 cup sour cream, and vanilla in medium bowl until combined.
3. Using stand mixer fitted with paddle, mix flour, sugar, baking powder, baking soda, and salt on low speed for 30 seconds to combine. Add butter and remaining 1⁄2 cup sour cream and mix until dry ingredients are moistened and mixture resembles wet sand, with few large butter pieces remaining, about 1-1⁄2 minutes. Increase speed to medium and beat until batter comes together, about 10 seconds; scrape down sides of bowl with rubber spatula. Lower speed to medium-low and gradually add egg mixture in 3 additions, beating for 20 seconds after each and scraping down sides of bowl. Increase speed to medium-high and beat until batter is light and fluffy, about 1 minute.
4. Using rubber spatula, spread 2 cups batter in bottom of prepared pan and smooth surface. Sprinkle evenly with 3⁄4 cup streusel filling. Repeat with another 2 cups batter and remaining 3⁄4 cup streusel filling. Spread remaining batter over filling, then sprinkle with streusel topping.
5. Bake until cake feels firm to touch and skewer inserted in center comes out clean (bits of sugar from streusel may cling to skewer), 50 to 60 minutes. Let cake cool in pan on wire rack for 30 minutes. Gently invert cake onto rimmed baking sheet (cake will be streusel side down); remove tube pan, place wire rack on top of cake, and invert cake streusel side up. Let cool to room temperature, about 2 hours, before serving.

SOUR CREAM COFFEE CAKE WITH CHOCOLATE CHIPS
Sprinkle 1⁄2 cup chocolate chips over bottom layer of batter before sprinkling with streusel and another 1⁄2 cup chocolate chips over middle layer of batter before sprinkling with streusel.

LEMON-BLUEBERRY SOUR CREAM COFFEE CAKE
Toss 4 ounces frozen blueberries with 1 teaspoon grated lemon zest in small bowl. Sprinkle 1⁄2 cup blueberries over bottom layer of batter before sprinkling with streusel and remaining 1⁄2 cup blueberries over middle layer of batter before sprinkling with streusel.

APRICOT-ALMOND SOUR CREAM COFFEE CAKE
Substitute 1 cup slivered almonds for pecans in streusel and 1⁄2 teaspoon almond extract for vanilla extract in batter. Spoon six 2-teaspoon mounds apricot jam over bottom layer of batter before sprinkling with streusel and another six 2-teaspoon mounds jam over middle layer of batter before sprinkling with streusel.