Ooey Gooey Butter Cake

Name: Ooey Gooey Butter Cake
Ingredients: 1½ cups granulated sugar; ¾ cup (1½ sticks) unsalted butter, room temperature; 1 teaspoon kosher salt; 1 large egg, room temperature; 1 cup all-purpose flour; ¼ cup light corn syrup or golden syrup; 2 tablespoons whole milk; 1 tablespoon vanilla extract; ¾ cup (1½ sticks) unsalted butter, room temperature, plus more for pan; 2½ cups all-purpose flour; 1 tablespoon baking powder; ¾ cup granulated sugar; ¾ cup (packed) light brown sugar; 3 large eggs, room temperature; 2 teaspoons vanilla extract; 1¼ cups sour cream; Powdered sugar (for serving)