Stir together spinach soufflé and next 3 ingredients with a fork just until dry ingredients are moistened.
Turn dough out onto a lightly floured surface; knead 8 to 10 times. Pat or roll dough to a 1/2-inch thickness; cut with a 2-inch round cutter. Place at least 1/2 inch apart on lightly greased baking sheets.
Bake biscuits at 425° for 10 minutes or until golden. Cool completely on wire rack.
Stir together 1/4 cup butter and 1 tablespoon mustard. Split biscuits, and spread cut sides evenly with butter mixture; fill biscuits evenly with thinly sliced ham.