Preheat the oven to 350°F . Coat a 9x13 baking dish with 2 teaspoons vegetable shortening. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment or a large mixing bowl with an electric mixer, beat the 3/4 cup unsalted butter until it is pale and fluffy. Add the 3/4 cup light brown sugar1/2 cup sugar, continue to beat for 2 more minutes.
Add the 2 eggs, one at a time, mixing between each addition.
Sift together the 2 cups flour, 1 teaspoon baking soda and 1/2 teaspoon salt. Gradually ad the dry ingredients to the wet ingredients until just mixed. Do not overmix.
Fold in the 1 1/2 cups butterscotch chips by hand.
Spread the batter into the prepared baking dish.
Bake for 30 to 35 minutes or until it passes the toothpick test.
Remove and allow to cool completely before cutting into 16 bars. Drizzle with the 1/2 cup caramel sauce and sprinkle with Fleur de sel, if desired.
If you've tried this recipe, come back and let me know how it was in the comments or star ratings.