Preheat your oven to 350°F (175°C) and prepare a 9×9-inch baking pan by lining it with parchment paper.
Combine 1 cup of all-purpose flour, 1/4 cup granulated sugar, and 1/4 teaspoon salt. Cut in 1/2 cup cold, cubed unsalted butter until it resembles coarse crumbs. Press into the bottom of the pan and bake for 15–18 minutes until lightly golden brown.
Wash and slice 3 to 4 large peaches, then toss with 1/2 cup granulated sugar, 2 tablespoons all-purpose flour, 1 tablespoon lemon juice, and 1/2 teaspoon vanilla extract until well coated.
Mix together 1/2 cup all-purpose flour, 1/4 cup granulated sugar, 1/4 cup brown sugar, 1/4 teaspoon cinnamon, and 1/4 teaspoon salt. Stir in 1/4 cup melted unsalted butter until crumbly.
Spread the peach filling evenly over the crust and sprinkle the crumb topping generously over the peach layer.
Bake at 350°F (175°C) for 45–50 minutes until golden brown and bubbly around the edges. Allow to cool completely before slicing into squares.