Original recipe yields 12 servings
Preheat the oven to 375 degrees F (190 degrees C). Coat an 8×8-inch baking pan with cooking spray.
Whisk flour, sugar, baking powder, and salt together in a bowl. Next, cut in the cold butter using 2 forks or a pastry cutter then slowly mix in the egg yolk and cold water. Don’t worry if the dough seems really crumbly; it should be!
Press 1/2 of the crumble mixture into the prepared pan to make the crust. Save the rest for the top of the bars.
Stir together peach slices, sugar, flour, lemon juice, vanilla extract, cinnamon, and nutmeg until combined. Evenly add peach filling to the top of the crust.
Sprinkle the remaining crumble over the peach filling.
Bake in the preheated oven until golden brown and set, 30 to 38 minutes. Cool bars to room temperature, then cut and serve.