Blueberry and Lemon Crumb Bars

Crust
1 1/2 c All-purpose flour unbleached
2 tb Sugar
2 ts Grated lemon rind
1/4 t Salt
1/2 c Cold butter cut in 1/4" slices
1 lg Egg yolk
1 t Vanilla extract
1 tb Cold water optional

Filling
1/2 c Sugar
2 tb All-purpose flour unbleached
1/4 t Freshly ground nutmeg
2 c Blueberries rinsed and sorted

Topping
5 tb Soft butter
1/2 c Packed light brown sugar
3/4 c All-purpose flour unbleached
Confectioner's sugar

Oven 400° F. Butter is unsalted unless otherwise stated. Lightly butter a 13- x 9-inch baking pan.

TO MAKE THE CRUST: Combine flour, sugar, lemon zest and salt in the bowl of a food processor. With the motor running, add pads of cold butter, a few at a time. In a small cup, stir together the egg yolk and vanilla. With the motor running, gradually add the yolk mixture; process until the mixture pulls together. If the mixture seems dry, add some to all of the cold water. Turn dough out (it will be crumbly) into the prepared pan; with floured fingertips, carefully press the dough into an even layer over the bottom of the pan.

TO MAKE THE FILLING: In a large bowl, stir together the sugar, flour and nutmeg until blended. Add the blueberries; stir to coat. Spread the blueberry-sugar mixture into an even layer over the crust.

TO MAKE TOPPING: Work the butter and sugar together with a wooden spool until blending. Using a fork, gradually add the flour, stirring until the mixture resembles coarse crumbs. Sprinkle the mixture evenly over the blueberries. BAKE for 15 minutes. Reduce the oven temperature to 350 degrees, and back for 25 to 30 minutes longer, or until the edges and topping are browned and the blueberries are cooked. Cool on a wire rack before cutting into bars. Lightly sprinkle with powdered sugar before serving.