Preheat oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, leaving an overhang for easy removal.

Prepare the shortbread mixture: In a large bowl or food processor, combine the flour, cold cubed butter, granulated sugar, and salt. Pulse or cut the butter into the dry ingredients until a crumbly, coarse mixture forms, similar to pea-sized pieces.

Press two-thirds (about 3/4 cup per 1/3 cup ratio if measuring by weight) of the mixture evenly into the bottom of the prepared baking pan to form the base crust. Bake the crust for 15 minutes until lightly golden.

While the base is baking, prepare the filling by gently combining the apricot preserves and lemon juice in a small bowl. Set aside.

Remove the partially baked crust from the oven. Spread the apricot filling evenly over the hot crust. Take the remaining one-third of the shortbread mixture and crumble it evenly over the apricot filling to create the topping.

Return the pan to the oven and bake for an additional 25-30 minutes, or until the topping is golden brown and the filling is bubbly. Let cool completely in the pan on a wire rack (at least 2 hours) before lifting out using the parchment overhang and cutting into 16 bars.