Cheddar Scones with Ham and Honey-Mustard Butter

4 cups all-purpose flour 2 tablespoons baking powder 1 1/2 teaspoons salt 1 stick (1/2 cup) cold unsalted butter 6 ounces coarsely grated extra-sharp Cheddar (about 1 1/2 cups) 1 cup whole milk 2/3 cup heavy cream 1 stick (1/2 cup) unsalted butter, softened 3 tablespoons coarse-grained mustard 3 tablespoons honey 6 large soft-leafed lettuce leaves such as Bibb 1/2 pound very thinly sliced cooked ham (preferably Black Forest)