Preheat the oven to 350°. Grease a 9-by-13-inch baking dish. In a medium bowl, using your fingers, combine 3 cups flour, the brown sugar and 1/2 teaspoon salt. Mix in all but 2 tablespoons butter until large crumbs form; set aside. In a small bowl, whisk together the remaining 2 tablespoons butter, the egg and the buttermilk.
In a medium bowl, stir together the remaining 1 1/2 cups flour, the granulated sugar, baking powder and remaining 1/2 teaspoon salt. Add the egg mixture and stir to form a thick, smooth batter. Fold about a third of the reserved crumb mixture into the batter; spread evenly into the prepared baking dish.
Scatter the cherries over the batter; sprinkle the remaining crumb mixture on top. Bake the cake until golden brown, 35 to 40 minutes. Transfer to a rack to cool for about 20 minutes before serving.