Preheat the oven to 350°F.

Line a 9x13-inch baking pan with parchment paper, and spray with nonstick cooking spray.

Place the softened butter, brown sugar, and vanilla extract into a large bowl. Use a mixer to cream together the butter and sugar on medium speed until pale and fluffy, about 1 minute. Add the egg and continue to beat on medium speed until light and fluffy, 30 seconds to one minute.

Add the flour, oats, baking soda, and salt to the bowl. Beat the mixture on medium speed for about 1 minute, until all ingredients are combined. Scrape down the sides of the bowl with a rubber spatula as needed.

Press about half of the dough into the baking pan. Use a rubber spatula or clean hands to press the dough into an even layer.

Bake on the middle rack of oven until the base is slightly puffy, about 10 minutes.

Carefully remove the baking pan from the oven. Sprinkle the chocolate chips and chopped nuts evenly over the par-baked dough. Pour the caramel sauce over the chocolate chips and nuts. Drop the remaining cookie dough by the spoonful on top of the caramel sauce, and gently flatten it with clean hands.

Return pan to oven and continue baking until the edges are golden brown and a toothpick inserted in the center comes out clean, 35-40 minutes.

Check to see that caramelitas are done. Remove from oven or add time as needed.

Allow the caramelitas to cool at room temperature for 15 minutes, then transfer the pan to the refrigerator for at least 1 hour before slicing and serving.

Lift the bars out of the pan by pulling up on the edges of the parchment paper. Slice into squares, and serve.