Set an oven rack in the lower third of the oven and preheat the oven to 350°F (175°C) (325°F [160°C] if using a dark pan).
In a medium bowl, whisk the flour, baking powder, baking soda, and salt just until lightly combined.
In the bowl of a stand mixer fitted with the flat beater, beat the butter on medium-high speed for 1 minute. Beat in the sugar slowly, taking about 2 minutes to beat it in, and then beat for another 2 minutes.
With the mixer off, pour in the egg, egg white, and vanilla and scrape down the sides of the bowl onto the egg mixture. Beat on medium speed for 1 minute, scraping down the sides of the bowl as needed.
With the mixer off between additions, add the flour mixture together with the sour cream in three parts. Beat each addition starting on low speed until the dry ingredients are moistened, then raise the speed to medium and beat for 15 seconds. Scrape down the sides of the bowl after each addition.
Spoon the batter into the cupcake liners to fill half full. Sprinkle each with 1 teaspoon of the streusel filling and drop a spoonful of batter on top. Use a small offset spatula or the back of a spoon to smooth the batter. The batter should fill the liner almost to the top.
Using a silicone spatula or spoon, scrape about half of the remaining batter into the prepared pan and smooth the surface evenly with a small metal spatula. Sprinkle the remaining streusel filling evenly over the batter, making a ring around the center of the batter to keep most of the streusel away from the outside and inside edges. Drop the remaining batter in large blobs over the filling and spread it evenly.
Bake until the cake just begins to come away from the sides of the pan, 20 to 30 minutes for the cupcakes and 45 to 50 minutes for the cake. In the cupcake liners, the cupcakes should spring back when pressed lightly in the center.
Let the cakes cool on wire racks in their pan and liners for 10 minutes. Coat a wire rack with nonstick baking spray. With a small metal spatula, loosen the top edges of the large cake and invert it onto the wire rack. Cool completely.