Begin by melting 2 teaspoons of unsalted butter in a skillet over medium heat. Once melted, add the peeled and diced Granny Smith apples along with 4 teaspoons of packed light brown sugar. Stir frequently until the apples soften and caramelize for about 5-7 minutes, then set aside to cool.
In a mixing bowl, whisk together 1 1/2 cups of all-purpose flour, 1 teaspoon of baking soda, 1 teaspoon of ground cinnamon, and 1/2 teaspoon of salt until well combined.
In another bowl, cream together 1 cup of unsalted butter with 1 cup of packed light brown sugar and 1/4 cup of granulated sugar using an electric mixer on medium speed until light and fluffy, about 3-4 minutes.
Add in 2 large eggs one at a time, beating well after each addition, followed by 2 teaspoons of vanilla extract. Continue mixing until everything is well combined.
Gradually add in the dry ingredient mixture to the wet ingredients while mixing on low speed just until combined; do not overmix! Then fold in the cooled caramelized apples along with 3 cups of rolled oats.
Preheat your oven to 350°F (175°C). Drop spoonfuls of dough onto a lined baking sheet spacing them about two inches apart. Bake for about 12-15 minutes or until golden brown around the edges but still soft in the center. Let cool before drizzling with a glaze made from powdered sugar mixed with water for added sweetness!