Preheat your oven to 350°F (175°C). Grease and line a 9x13-inch baking pan with parchment paper, leaving some overhang for easy removal.
In a mixing bowl, whisk together the flour, granulated sugar, baking powder, baking soda, and salt until well combined.
In a separate bowl, cream the softened butter using a rubber spatula or mixer. Then, add the egg and vanilla extract, and mix until smooth.
Gradually combine the dry ingredients with the wet mixture until just incorporated, being careful not to overmix.
Reserve about 1 cup of the cookie dough for the streusel topping, and spread the remaining dough evenly in the bottom of the prepared baking pan.
Evenly distribute the diced peaches over the cookie base.
Crumble the reserved cookie dough over the peaches to form the streusel topping.
Bake in the preheated oven for 25-30 minutes, or until the tops are golden brown and a toothpick inserted in the center comes out clean.
While the bars bake, prepare the almond glaze. In a small bowl, whisk together the powdered sugar, almond milk, and almond extract until smooth and drizzle-worthy.
Once the bars are out of the oven, let them cool in the pan for about 10-15 minutes. Then, lift the bars out using the parchment paper and allow them to cool completely on a cooling rack.
Once cooled, drizzle the almond glaze over the bars, slice them into squares, and serve.