Preheat oven to 350°F. Line a 9x13 pan with foil or parchment, and spray with non-stick spray.
Using a hand mixer or stand mixer fitted with the paddle attachment, combine granulated sugar, baking powder, flour, and salt. Add butter, egg, vanilla, and almond extract. Beat on low speed until the butter is evenly distributed in small pieces and the mixture is crumbly.
Dump a little more than half of the mixture into the bottom of the prepared pan. Use your hand or the bottom of a measuring cup to evenly press the dough into the pan. Stir sliced almonds into the reserved mixture (for topping).
Gently stir together all ingredients until combined.
Spread the peaches evenly over the crust, then crumble the reserved dough over the top of the peaches.
Bake for approximately 40 minutes, until the top is light golden brown, and the peach juices are bubbling. Transfer pan to a rack to cool before cutting into squares. I like to store these in the fridge. They can also be frozen.
How to peel a peach:
If you'd like to drizzle the bars with icing: whisk together 1/4 cup powdered sugar with a splash of milk and a drop of vanilla extract. Adjust to get your desired consistency by adding more sugar or milk.