Whisk 2 cups flour, 1 tablespoon each baking powder and sugar and 1/2 teaspoon each mustard powder and kosher salt in a large bowl. Stir in 3/4 cup shredded cheddar. Cut in 6 tablespoons diced cold butter until it is in pea-size pieces; stir in 1 cup heavy cream whisked with 3 tablespoons grainy mustard. Divide into 8 mounds on a parchment-lined baking sheet; brush with more cream. Bake at 425 degrees F until golden, 20 to 25 minutes.