Peel peaches if desired. Slice into roughly even slices (about 8-10 per peach). Measure out 4-5 cups of sliced peaches. Keep any liquid that accumulates.Fresh Peaches: Place sliced peaches and accumulated liquid, ½ cup sugar, ¼ cup brown sugar, and ¼ teaspoon cardamom in a medium mixing bowl and stir to combine. Set aside.Canned Peaches: Do not drain peaches; you will use the liquid. For peaches in heavy syrup, fold in a ¼ teaspoon of cardamom. For peaches in light syrup, fold in 2 tablespoons brown sugar and a ¼ teaspoon of cardamom.
Preheat oven to 350℉ (177℃). Slice butter and place in a 9x13 glass baking dish. Place the baking dish in the oven while it preheats.
Remove baking dish from oven when all the butter has melted.
Mix the batter while the butter is melting.In a medium mixing bowl, whisk together flour, ¼ cup each sugar and brown sugar, ½ teaspoon cardamom, baking powder, and salt. Set aside.In a large mix-and-pour bowl, beat the egg, and then whisk in the milk.Whisk the dry ingredients into the wet ingredients until the mixture is smooth.
Slowly pour the batter in over the melted butter in thin ribbons, covering the bottom of the baking dish. Use a spatula only as necessary to distribute the batter evenly. (Avoid stirring. It's totally fine for the batter to have little holes in it. )The baking dish with the melted butter should still be very warm when you pour in the batter; 5-10 minutes out of the oven is perfect. Do not pour the batter into bubbling butter - the pan will be too hot.
Carefully spoon the prepared peaches and any accumulated juice evenly over the top over the top of the batter.(Canned peaches only: Use up to ¾ cup of the peach liquid.)
Bake at 350℉ (177℃) for 45-55 minutes. The batter will rise to the top during baking, surrounding the fruit. Bake until the top is golden brown and the center bounces back when gently pressed.
Top Tip: Taste your peaches before baking — reduce sugar if they’re very sweet, or add a little more if they’re tart. For a sweeter crust, add 1 tablespoon each of granulated and brown sugar to the batter.