Preheat the oven to 350°F.

Line an 8-inch square baking pan with foil, leaving a 2-inch overhang on all four sides. Grease the foil with additional butter or nonstick cooking spray.

Combine the flour, baking soda, salt, rolled oats, and light brown sugar in a large bowl. Mix well to combine. Add the butter and cut it into the flour mixture using a pastry blender or fork until the mixture is very crumbly and holds together when squeezed.

Press two-thirds of the crumb mixture evenly into the bottom of the lined pan. Spread the jam in an even layer over top, leaving a ½-inch border on all four sides.

Sprinkle the remaining crumb mix all over the top. Press it gently into the jam layer.

Bake for 35 minutes or until the crumble is golden brown and the jam is bubbly. Let the bars cool in the pan completely, about 1½ hours. Remove from the pan by lifting out the foil. Remove the foil from the slab and cut into 16 squares.