01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving overhang for easy removal.
02 - In a medium bowl, combine flour, granulated sugar, salt, and cold butter. Mix with a pastry cutter or fingers until mixture forms coarse crumbs. Press mixture evenly into the base of the prepared pan and bake for 12 to 14 minutes, or until lightly golden.
03 - In a mixing bowl, beat together ricotta cheese, granulated sugar, egg, vanilla extract, and lemon zest until mixture is smooth and well combined.
04 - In a small saucepan over medium heat, stir together cherries, granulated sugar, cornstarch, and lemon juice. Cook, stirring occasionally, until mixture thickens and cherries release juices, about 5 minutes. Allow to cool slightly.
05 - Combine flour, brown sugar, and cold butter in a bowl. Rub together with fingertips until coarse crumbs form.
06 - Spread ricotta filling evenly over baked crust. Spoon cherry mixture over ricotta layer. Sprinkle crumble topping uniformly over the cherries.
07 - Bake for 25 to 28 minutes, until topping is golden and filling is set. Cool completely in pan, then lift bars out with parchment and slice into portions.