Preheat your oven to 350°F (175°C). This ensures that your bars will bake evenly.
Grease your 9x13-inch baking pan with butter or line it with parchment paper for easy removal later.
In a medium bowl, whisk together the flour, baking soda, ground cinnamon, and salt. Set aside.
In a large mixing bowl, beat the room-temperature unsalted butter and packed dark brown sugar together until light and fluffy, about 2-3 minutes. This step is crucial for achieving that chewy texture!
Add the large egg and vanilla extract to the butter-sugar mixture, mixing until well combined.
Gradually add the dry ingredients to the wet mixture, mixing until just combined. Be careful not to overmix!
Add the whole or low-fat milk and stir until incorporated. This will help keep your bars moist.
Gently fold in the dried cranberries or sour cherries, shredded coconut, rolled oats, and milk chocolate chips until evenly distributed throughout the batter.
Pour the batter into the prepared baking pan, spreading it out evenly with a spatula.
Bake in the preheated oven for 25-30 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out clean.
Allow the bars to cool in the pan for about 10 minutes, then transfer to a cooling rack to cool completely before cutting into squares.
