Winter. Still comfort food days and nothing is more comforting than Blueberry Coffee Cake. This one has a big punch of lemon, which makes it bright and clean.
1 cup (2 sticks) unsalted butter, softened
3 cups all-purpose flour
1 1/2 cups old-fashioned rolled oats (not quick oats)
1 1/3 cups packed light brown sugar
1 teaspoon salt
1 teaspoon baking powder
1 large egg, separated
1 (14 ounce) can sweetened condensed milk
1/2 cup freshly squeezed lemon juice
2 teaspoons grated lemon zest
2 1/2 cups fresh blueberries
Preheat oven to 350F. Create an aluminum foil sling for your 9×13 inch baking pan. Spray foil sling generously with baking spray.
In a large bowl, whisk together flour, oats, sugar, salt, and baking powder. Using a pastry cutter (or your fingers), blend the butter completely into the flour mixture. Transfer 2 cups of the crumb mixture to another bowl and reserve for the topping.
Blend the egg white into the remaining crumbs and then press the mixture into the bottom of the pan to form a level crust. You can use the bottom of a measuring cup to even it out. Bake the crust 10-12 minutes, or until it starts to form a dry top.
Meanwhile, in a medium bowl, whisk together the condensed milk, lemon juice and zest, and egg yolk. Let mixture stand for 5 minutes (it will begin to thicken).
Sprinkle blueberries evenly over hot crust and then drop spoonfuls of the lemon mixture over the blueberries. Spread gently with a spatula to distribute as evenly as you can. Bake until lemon mixture begins to form a shiny skin, 7 to 8 minutes.
Sprinkle reserved crumble topping over the lemon-blueberry layer, pressing the streusel between your fingers into small lumps as you sprinkle. Bake until filling is bubbly at the edges and the topping is brown, 25 to 30 minutes.
Let bars cool in the pan on a rack until just warm, about an hour. Carefully lift them out of the pan using the foil sling and transfer to a wire rack to cool completely. Remove foil and cut into 24 bars when cool.