Preheat the oven to 375°F (190°C). Line an 8x8-inch square pan with parchment paper and lightly spray or grease the paper.
Pulse 1/4 cup pecans in a food processor until coarse crumbs form; set aside.
Make the crumb base: in a bowl whisk together 1 1/2 cups all-purpose flour, 1/2 cup light brown sugar, the pecan crumbs, 1/2 teaspoon baking soda, 1/2 teaspoon baking powder, and 1/4 teaspoon salt.
Add 1/2 cup melted, cooled butter to the dry mixture and stir until the butter is fully incorporated; the mixture will be crumbly.
Reserve 3/4 cup of the crumb mixture for the topping, then press the remaining crumbs evenly into the bottom of the prepared pan to form the crust.
Prepare the sour cream layer by whisking together 1/2 cup sour cream, 1/4 cup granulated sugar, 1 tablespoon all-purpose flour, 1 egg, and 1/2 teaspoon vanilla extract until smooth.
Pour the sour cream mixture over the pressed crust and spread it into an even layer.
Spoon the 21-ounce can of cherry pie filling over the sour cream layer and gently swirl with a spoon to slightly marble the layers.
Sprinkle the reserved 3/4 cup crumb mixture evenly over the cherries, then bake for 25–28 minutes or until the top is golden brown.
Cool completely in the pan on a wire rack, then lift out using the parchment and cut into 8 bars to serve.