Preheat the oven to 325°F. Line an 8×8-inch metal baking pan with parchment paper, leaving a bit of overhang on the sides. This will make lifting the bars easier once they’re baked and cooled.

In a large bowl (or using a stand mixer with the paddle attachment), cream together the softened butter, granulated sugar, and brown sugar until smooth. Add the vanilla extract, baking powder, and apple cider vinegar, stirring well to combine.

In a separate medium bowl, whisk together the flour, salt, and baking soda. This will ensure the dry ingredients are evenly distributed.

Gradually add the flour mixture to the butter mixture, stirring just until combined. The dough will be a bit crumbly. Gently fold in 1 cup of the chopped candy pieces.

Press the dough evenly into the prepared baking pan. Scatter the remaining chilled candy pieces over the top, pressing down slightly to ensure they stick.

Bake in the preheated oven for about 22 minutes, or until the edges are lightly golden brown and the bars are set.

Remove the pan from the oven and let the bars cool on a wire rack. Once completely cool, lift them out using the parchment overhang and transfer to a cutting board. Cut into squares and serve at room temperature.