Sweet, fruity jam bars with a buttery oat crust and crumble topping are a simple, family-friendly dessert. These easy, versatile bars work beautifully with any favorite jam or preserves.
Preheat the oven to 350°F and line an 8-inch square baking pan with parchment paper, leaving an overhang for easy removal.
In a large bowl, combine the old-fashioned oats, flour, packed brown sugar, baking powder, and fine salt.
Melt the unsalted butter in a small saucepan over low heat, then stir in the vanilla extract. Pour the wet mixture into the dry ingredients and mix until crumbly.
Press about two-thirds of the dough firmly into the bottom of the prepared pan to form an even crust. Spread the jam evenly over the crust, leaving a ¼-inch border.
Crumble the remaining oat mixture evenly over the jam layer, gently pressing for better adhesion. Bake for 28–32 minutes until the top is golden and the edges are set.
Cool in the pan for at least 1 hour before lifting out and slicing into bars for clean edges and optimal texture.