Preheat your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, leaving an overhang on the sides to easily lift the bars out later. Lightly grease the parchment paper.

In a large mixing bowl, cream together the softened unsalted butter and packed light brown sugar until light and fluffy.

In a separate medium bowl, whisk together the all-purpose flour, old-fashioned rolled oats, baking soda, and salt. Gradually add the dry ingredients to the butter mixture, mixing until just combined and a crumbly dough forms. Do not overmix.

Press about two-thirds of the oat crumb mixture evenly into the bottom of the prepared 9x13 inch baking pan. Reserve the remaining one-third for the topping.

Bake the base layer for 10-12 minutes, or until lightly golden brown. While the base bakes, prepare the caramel.

If using unwrapped caramels, combine them with 2 tablespoons of milk in a microwave-safe bowl. Microwave in 30-second intervals, stirring after each, until smooth and melted (alternatively, melt in a saucepan over low heat). If using dulce de leche, no additional prep is needed.

Remove the baked base from the oven. Evenly sprinkle the semi-sweet chocolate chips over the warm base. Pour or dollop the melted caramel (or dulce de leche) over the chocolate chips, spreading gently if needed.

Crumble the remaining one-third of the oat crumb mixture evenly over the caramel layer.

Return the pan to the oven and bake for another 20-25 minutes, or until the topping is golden brown and the caramel is bubbly.

Let the bars cool completely in the pan on a wire rack for at least 2-3 hours before lifting them out using the parchment paper overhang. Once cooled and firm, cut into 16 squares.