Preheat oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper, leaving an overhang. Cream softened butter and granulated sugar until light and fluffy, then beat in vanilla extract.

Gradually add all-purpose flour and salt to the creamed mixture, mixing until a soft dough forms. Press the dough evenly into the prepared baking pan.

Bake the shortbread for 20-25 minutes until the edges are lightly golden. Remove from the oven and let it cool completely in the pan on a wire rack.

Combine granulated sugar, water, and corn syrup (if using) in a medium heavy-bottomed saucepan over medium heat, stirring until sugar dissolves, then stop stirring and cook until it turns a deep amber color (8-12 minutes). Remove from heat and carefully whisk in warm heavy cream.

Stir in butter and vanilla extract until smooth, then stir in the salt. Let the caramel cool for 5-10 minutes until warm and pourable but not blistering hot.

Once the shortbread is completely cool, pour the warm caramel evenly over the top and spread to the edges. Allow the caramel to set at room temperature for at least 30 minutes, or refrigerate for 15-20 minutes to speed up setting.

Melt chocolate chips with coconut oil (if using) in a microwave in 30-second intervals (stirring between) or in a double boiler until smooth. Pour the melted chocolate over the set caramel layer, spreading evenly to cover the entire surface.

Place the pan in the refrigerator for at least 1-2 hours until the chocolate and caramel are firm enough to cut.

Lift the slab from the pan using the parchment paper overhangs and place on a cutting board. For clean cuts, dip a sharp knife in hot water and wipe it dry before each cut, then cut into bar shapes or squares and serve.