Preheat oven to 350°F. Line 8 inch pan with nonstick foil.

Combine butter, flour, sugar and vanilla in a large mixing bowl. Beat for 1 minute on medium speed until the batter starts to come together. While together, but still crumbly, transfer dough into the prepared pan and press evenly to make the base. Bake for 20-25 minutes, or until golden.

Meanwhile, make the filling. Place the butter, sugar, dark corn syrup, and condensed milk in a medium saucepan over medium-low heat. Stir frequently. Once the sugar dissolves, increase heat and bring milk mixture to a boil, then reduce heat back to medium-low heat. Cook, stirring frequently, for 8-10 minutes until the mixture becomes thick and begins to pull away from the sides of the pan.

Pour over the baked shortbread base and let cool for 15-30 minutes. Place in the refrigerator to cool, and firm, completely.

Once firm, melt the chocolate in the microwave. Cool slightly. Carefully pour over the caramel. Use an off-set spatula to even the layer and make any desired pattern.

Chill to set. Cut into desired bars. Store in an airtight container for up to a week. Makes about 16, 4-inch sticks.