½ cup light brown sugar (packed)
1½ teaspoons ground cinnamon
2 large eggs
½ cup granulated sugar
½ cup (1 stick) unsalted butter, melted and slightly cooled
½ cup milk
2 teaspoons vanilla extract
1½ cups all-purpose flour, spooned into measuring cup and leveled-off
½ teaspoon salt
1½ teaspoons baking powder
1 cup peeled, cored, and finely diced tart baking apples, from 1 apple (preferably Granny Smith)