Preheat oven to 350°F and line an 8×8 baking pan with parchment paper. In a large mixing bowl, use a hand mixer or stand mixer to beat together the melted butter, brown sugar, and granulated sugar for 2–3 minutes until smooth and slightly thickened. This step helps create a soft, chewy texture. Add the applesauce and vanilla extract, mixing until fully combined.
In a separate mixing bowl, whisk together the flour, cornstarch, and baking soda. Gradually add the dry ingredients into the wet ingredients, mixing until a thick dough forms. Do not overmix.
Fold in the chocolate chips until evenly distributed.
Press the dough evenly into the prepared pan, smoothing out the top.
Sprinkle red, white, and blue sprinkles over the top and gently press them into the dough. Bake for 18–20 minutes, until the edges are set and lightly golden while the center remains soft.
Allow the bars to cool completely in the pan before slicing into squares.