Heat oven to 400°F

Cook potatoes in microwave 5-7 mins

Cook yams in microwave 7-9 mins

Brown beef in skillet

Add tomatoes, cinnamon and cumin. Simmer 3 mins

Combine flour, milk, butter and nutmeg in a saucepan over medium heat stirring constantly

Bring to boil and simmer one minute

Season with salt and pepper

Remove from heat and whisk in egg yolk

Thinly slice potatoes

Place half of potatoes and yams on bottom of 2 quart casserole

Layer meat then remaining potatoes and yams

Pour sauce on top

Sprinkle with cheese

Bake for 30 mins