Preheat the oven to 350ºF (180ºC). Line a 6-serving shallow jumbo muffin pan* with jumbo muffin liners.** Jumbo muffin liners will fit by pressing them around the inside bottom edges.
In a medium-sized bowl, whisk together the flour, baking powder and salt until well blended.
In a large bowl, cream the butter, sugar and lemon zest with an electric mixer on medium speed, until pale and fluffy. Beat the egg and egg yolk into the butter mixture in 2 separate additions, making sure each addition is well incorporated. Beat in the extracts until combined.
In a small bowl, whisk the milk and sour cream together. With the mixer on low speed or by hand, mix the flour mixture into the batter in 2 additions alternating with half of the milk mixture after each addition. Mix just until combined.
Transfer the batter to the prepared baking pan, evenly distributing the batter and filling the cups about half full.
In a medium-sized bowl, toss the blueberries with 1 teaspoon of flour and place them into the cups on top of the batter, about 1 ounce (28g) in each. Top each one with crumb topping.
Bake until a toothpick inserted into the center of the cakes comes out clean, about 25-30 minutes. Let the cakes cool in the pan for 5 minutes, then transfer them to a cooling rack to cool completely.