For stronger ginger flavor, replace the dried ginger with three tablespoons grated peeled fresh ginger and three tablespoons minced crystallized ginger. If you don’t own an 11 by 7-inch pan, you can bake the batter in a 9-inch-square pan.
Apple Topping
4 tablespoons unsalted butter , melted
3/4 cup light brown sugar
3 tart apples (such as Granny Smith or Jonathan), peeled, halved, cored, and sliced thin
Gingerbread
2 1/4 cups unbleached all-purpose flour , sifted
1/2 teaspoon baking soda
1/2 teaspoon table salt
2 teaspoons ground ginger
1 teaspoon ground cinnamon
1/2 teaspoon ground cloves
1/2 teaspoon ground nutmeg
1/2 teaspoon ground allspice
1 teaspoon Dutch-processed cocoa powder
8 tablespoons unsalted butter , melted, then cooled to room temperature
3/4 cup unsulphured molasses
3/4 cup granulated sugar
1 large egg
1/2 cup buttermilk
1/2 cup milk
1. For the Apple Topping: Adjust oven rack to middle position and heat oven to 350 degrees. Grease sides of 11 by 7-inch baking pan. Pour melted butter into pan; spread brown sugar evenly over pan bottom. Arrange apple slices, overlapping slightly upon brown sugar mixture.
2. For the Gingerbread: Whisk together flour, baking soda, salt, ginger, cinnamon, cloves, nutmeg, allspice, and cocoa in medium bowl.
3. Beat butter, molasses, and sugar in large bowl with electric mixer on medium speed until combined. Beat in egg until incorporated. Gradually add buttermilk and milk until combined.
4. Add dry ingredients to liquid; beat on medium speed until batter is smooth, about 1 minute, scraping down sides of bowl with rubber spatula as needed. Do not overmix. (If using fresh ginger, batter will be lumpy.) Pour batter over apple slices.
5. Bake until top springs back when lightly touched, and edges have pulled away from the pan sides, 50 to 60 minutes. Set pan on wire cake rack and let cool for 5 minutes, invert onto serving plate, cut into squares, and serve.