• Sauté Vegetables: Heat oil in a large skillet over medium-high. Sauté onions, carrots, celery, and bell pepper for 3 to 5 minutes until tender. Stir in chopped tomato and garlic, and season with salt, black pepper, paprika, and savory. Transfer to a 9x13 casserole dish.
• Cook Ground Beef: Brown beef in the same skillet for 5 minutes, breaking it up as it cooks. Season with salt, black pepper, paprika, savory, and cumin. Add to the casserole dish.
• Cook Potatoes: In the same skillet, cook potatoes in two batches with oil, seasoning each batch with salt, paprika, black pepper, and savory. Cook covered for 10 minutes, stirring occasionally. Add to the casserole dish.
• Combine and Bake: Mix everything in the casserole dish and spread evenly. Pour 1 cup of water over the mixture. Bake in a preheated oven at 375 degrees Fahrenheit for 40 minutes.

Topping

• Make topping: While the moussaka is baking, make the topping. Beat 4 egg whites until fluffy. In a separate bowl, beat 4 egg yolks with 4 Tbsp water. Fold in the yogurt, milk, egg yolks and baking soda into the egg whites. Season with salt and ground black pepper.
• Bake: Increase the oven temperature to 400 degrees Fahrenheit. Spread topping over the baked moussaka, sprinkle with shredded cheese, and bake for 10-15 minutes until golden.
• Serve: Let moussaka rest for about 10 - 15 minutes before cutting. Serve warm.