Preheat the oven: Set your oven to 375°F. If using a glass pan, reduce the temperature by 25°F.

Prepare the crust: To prepare the crust, whisk together the sugar, flour, baking powder, and salt in a large mixing bowl. Work the cold butter into the dry ingredients with a pastry cutter—or briefly pulse in a food processor—until you achieve a crumbly, sand-like texture. Stir in the beaten egg until a crumbly dough forms.

Make the filling: In another bowl, mix sugar, cornstarch, and cardamom. Gently fold in the diced peaches and lemon juice, making sure to coat the fruit evenly while keeping the pieces intact.

Assemble the bars: For assembly, set aside ¼ cup of the crust mixture to use as a crumble topping. Press the remaining dough evenly into a greased 9×13-inch baking dish. Spread the peach mixture over the crust, then sprinkle the reserved dough on top.

Bake: For a metal pan, bake for 40–45 minutes at 375°F. For a glass pan, bake for 50–55 minutes at the adjusted lower temperature, until golden and bubbly.

Cool & ice: Let the bars cool completely. In a small bowl, whisk together powdered sugar, almond extract, and milk. Adjust the consistency as needed. Drizzle over the cooled bars and let set before cutting into 2-inch squares.