Ingredients
1 cup unsalted butter, softened
3 cups all-purpose flour
1 1/2 cups old-fashioned rolled oats
1 1/3 cups packed light brown sugar
1 tsp. baking powder 1 tsp. salt
1 large egg, separated
14 ounce can sweetened condensed milk
1/2 cup freshly squeezed lemon juice
zest of one lemon zest
2 1/2 cups room-temperature blueberries, washed and drained on paper towels

1. Preheat oven to 350°F. Spray a 9×13 inch glass baking dish with non-stick cooking spray. (make sure to get the bottom and sides!)
2. In a large bowl, whisk together flour, oats, sugar, salt and baking powder. Using a pastry cutter (or two knives), blend the butter completely into the flour mixture (you want it to be crumbly).Reserve two cups of the crumb mixture (this will be use for topping)
3. Blend the egg white into the remaining crumbs and then press the mixture into the bottom of the pan to form a level crust.
4. Bake the crust 10-12 minutes, or until it starts to form a dry top.
5. Meanwhile, in a medium bowl, whisk condensed milk, lemon juice, zest and egg yolk. Let mixture stand for 5 minutes (it will begin to thicken).
6. Sprinkle blueberries evenly over hot crust and then drop spoonfuls of the lemon mixture over the blueberries. Spread gently w/ a spatula for even distribution. Bake until lemon mixture begins to form a shiny skin. (7 to 8 minutes.)
7. 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.
8. Let bars cool in the pan on a rack until just warm, about an hour. Cut into 24 bars when cool. (If you have time to chill the bars, they’re easier to cut cleanly when chilled).
Yield: Approximately 24 bars