Design Eat Repeat

0 Preheat oven to 350°F.
16 Chop caramels into smaller pieces (for Kraft caramels, I cut each into 8 smaller pieces).
2 In a medium-sized microwave-safe bowl, melt unsalted butter [adjustable](¾ cup, 1 ½ sticks)[/adjustable] 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.)
3 [adjustable]Add in light brown sugar (¾ cup) and granlated sugar (½ cup) use a spatula to stir until combined (* do not use a mixer!). Add in egg (1 large), extra egg yolk and vanilla extract (2 teaspoons). Mix until combined.[/adjustable]
11 [adjustable]Stir in baking soda (1 teaspoon), baking powder (¼ teaspoon), and salt (1/2 teaspoon). [/adjustable]
14 [adjustable]Add in all-purpose flour (2 cups*) and mix until all the flour disappears into the dough. [/adjustable]
15 [adjustable]Add mix-ins of choice. I used the following: semi-sweet chocolate chips (½ cup), milk chocolate chips (½ cup), pretzel pieces (½ cup), caramel pieces (½ cup), and sprinkles (2 tablespoons).[/adjustable]
4 Press dough into a greased or parchment-lined metal 9x13" pan until smooth. If desired, press on a few extra mix-ins to the top for aesthetics.
6 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. 
12 Allow the cookie bars to cool completely before removing from pan. Slice into 12 large, 24 medium, or 48 bite-sized squares (photo reference in blog post), then enjoy! To keep fresh, cover pan with saran wrap or place bars in airtight continer for up to 3 days (after that they start to dry out). See notes below for freezing tips.