Blueberry Crumb Bars

Ingredients

• 2 1/2 cups all-purpose flour
• 1 cup sugar
• 2 teaspoons lemon zest
• 1/2 teaspoon kosher salt
• 1 cup cold unsalted butter, cubed
• 1 large egg yolk
• 3 cups fresh or frozen blueberries
• 3 tablespoon granulated sugar
• 1 1/2 teaspoons cornstarch
• 1 tablespoon lemon juice
• 1 teaspoon lemon zest

Directions

1. Heat the oven to 375 degrees F. Butter a 9x9 inch pan, then line it with parchment so you have extra paper hanging over 2 sides. In a food processor, pulse the flour, sugar, lemon zest, and salt a few times until mixed. Add the butter and pulse again until the mixture looks fine and sandy, with the butter worked all the way in.
2. Add the egg yolk and pulse 10 to 15 times, just until it is mixed through. Pinch a bit in your hand; it should clump together. If it still feels too dry, scatter 1 tablespoon of water over the mixture and pulse a few more times. No food processor? Use a pastry blender or fork to work the butter into the flour mixture. It takes a little more patience, but it gets you there.
3. Take out about 1/3 of the crumb mixture and pack it lightly into a bowl; this helps you get those nicer, chunkier crumbs for the top. Cover the bowl and chill it for at least 15 minutes, or leave it in the refrigerator until you need it.
4. Press the remaining 2/3 of the crumbs firmly into the prepared pan to make the bottom layer. A measuring cup is handy here, because it helps you press everything down evenly and compact the crust.
5. In a mixing bowl, toss the blueberries with the sugar, cornstarch, lemon juice, and zest until the berries are coated. Spoon them over the crust in an even layer. Take the chilled crumbs from the refrigerator, break them up with your fingers, and scatter them over the blueberries.
6. Bake for 1 hour and 5 minutes, until the blueberry layer is bubbling and the crumb topping has turned golden. Take the pan out of the oven and set it on a cooling rack. Let the bars cool completely in the pan, at least 2 hours, then use the parchment to lift them out and cut them into squares. After they are cool and sliced, move the bars to an airtight container and keep them at room temperature for about a week.