In a 9x13 casserole dish layer chicken, ham, leeks cheese in alternating layers. Season with salt and pepper and nutmeg.
In a medium saucepan melt butter over mediom heat. Stir in flour and mustard. Add the broth and half&half slowly and with a wooden spoon stir until thickend. Pour sauce over meat and leek layer.
Crust - Blend all the dry ingredients in medium bowl. Melt the butter in the microwave. Measure out the buttermilik and pour the butter into it.Make a well in the centre of the dry ingredients and pour liquid in. Stir to make a soft dough.
Drop the dough in "globs" to cover evenly, leaving a bit of space for the steam to escape. Bake incovered for 25 minutes or until bubbly, puffy and golden.