In a small pan or pot over low heat combine half-and-half and cream cheese. Melt cream cheese and season sauce with salt, pepper and nutmeg, if using.
Heat a 12-inch nonstick skillet over moderate heat and use a very thin spatula or fish spatula to manipulate the eggs. Swirl in butter to coat the pan and when it foams add eggs and let them settle. Gently lift pan a bit and begin swirling the eggs to edges of bottom of pan, forming a thin omelet about 10 inches wide. When the eggs begin to dry on top and steam, a few bubbles will form. Remove pan from heat and top with sauce, covering the surface, then Gruyere and ham working down the center but from edge to edge. Fold in sides of crepe, like swaddling a doll. Carefully transfer to plate.