In a medium-sized microwave-safe bowl, melt ¾ cup unsalted butter (not margarine), 1½ sticks) for 20-30 seconds until JUST melted. (If your butter is steaming, let it cool down for a few minutes. Butter that is too hot can result in greasy bars and/or will cause the eggs to cook.)
Add in¾ cup light brown sugarand ½ cup granulated sugarand use a spatula to stir until combined (*do not use a mixer!). Add in 1 large egg + 1 yolk and 2 teaspoons vanilla extract. Mix until combined.
Stir in 1 teaspoon baking soda, ¼ teaspoon baking powder, and ½ teaspoon kosher salt.
Add in 2 cups all-purpose flour, and ¾ cup graham cracker crumbs and mix until all the flour disappears into the dough.
Addmix-ins ½ cup cinnamon sugar pretzels, broken and part of the caramel pieces (8 Werther's caramel apple soft caramels, torn).
Press dough into a greased or parchment-lined metal 9x13" pan until smooth. Press the other torn 4 Werther's caramel apple soft caramels, a few extra pieces of pretzel & extra graham cracker pieces to press on top for aesthetics. I like to pull apart the caramels into little strips so that you get a marbling look on top.
Bake at 350°F for 16-18 minutes until edges and top are lightly golden brown and center no longer looks wet; some ovens may need up to 20 minutes. Remove from oven and place entire pan on a cooling rack.
Allow the cookie bars to cool completely before removing from pan. Slice into 24 squares, then enjoy! To keep fresh, cover pan with saran wrap or place bars in airtight container for up to 3 days (after that they start to dry out). See notes below for freezing tips.