Preheat the oven to 375°F and grease a 9x13-inch baking dish with 4 tablespoons of butter, leaving any excess butter in the dish.
4 tablespoons salted butter
In a large bowl, whisk together the granulated sugar, brown sugar, flour, cinnamon, and salt. Stir in the lemon juice, orange zest, and vanilla extract. Gently stir in the drained peaches. Pour this mixture into the prepared baking dish and bake for 15 minutes.
1 cup granulated sugar, ¼ cup light brown sugar, ¼ cup all-purpose flour, 1 teaspoon ground cinnamon, ½ teaspoon salt, 1 tablespoon lemon juice, 1 teaspoon orange zest, 3 (28oz.) cans sliced peaches, ½ teaspoon vanilla extract
While the peaches are baking, prepare the topping. Be prepared to make the topping while the peaches are baking (the topping must be added to the peaches when they are hot. If you are not going to make the topping right away, just set the peaches aside.)
Pour the remaining 1 tablespoon of lemon juice into the ½ cup of milk. Set this aside and allow this to sit for at least 5 minutes, while you are getting the other topping ingredients mixed.
1 tablespoon lemon juice, ½ cup whole milk
Add the flour, sugar, and baking powder to a food processor and pulse together.
2 cups all-purpose flour, 1 cup granulated sugar, 2 teaspoons baking powder
Add in the cold butter and pulse just until the mixture is crumbly (do not overmix).
¾ cup salted butter
Whisk the vanilla extract into the milk mixture (it will have thickened and resemble buttermilk). Add this mixture to the food processor. Pulse just until the crumbs are moistened. Spoon or sprinkle this crumbly topping onto the peaches as soon as they come out of the oven. If you allow the peaches to cool at all, the topping will not bake properly. It is okay if there is some space between the spoonfuls of topping.
1 teaspoon vanilla extract
Bake for 35 to 40 minutes until the top is golden brown. If it starts to get too dark, cover with aluminum foil for the rest of the baking time.