Preheat oven to 350°F.
Liberally grease a 9x13” baking dish with butter.
Lay the potato slices evenly in the bottom of the baking dish, drizzle with olive oil, and season to taste with salt and pepper.
Once the oven has reached temperature, bake the potato slices for 30 minutes.
Line a cookie sheet with paper towels, then arrange the eggplant slices in a single layer. Sprinkle salt liberally all over and allow the eggplant to sit for 30 minutes. The salt will draw moisture out of the eggplant.
While the eggplant rests and the potatoes cook, get started on the meat sauce.
Add some olive oil to a large skillet and heat over medium-high.
Add the diced onions and cook until soft.
Add the ground beef and cook until no pink remains.
Add the garlic and cook another 3 minutes.
Add the tomato paste and cook again another 3 minutes.
Pour in the red wine and stir until combined.
Add the crushed tomatoes and broth, stirring again.
Add the bay leaves and seasonings, stir, and once the sauce is bubbly, turn down the heat to a simmer.
Allow the sauce to simmer, uncovered, until most of the liquid has evaporated (about 30 minutes).
While the sauce simmers, start making the béchamel.
Add the butter to a medium saucepan and heat over medium.
Once the butter is melted, add the flour and cook for 5 minutes, stirring constantly.
Heat the milk in the microwave until warm or hot. Slowly pour into the roux (flour mixture), stirring constantly. Take your time doing this; it will help avoid lumps.
Once all the milk has been added, drop the egg yolks, one at a time, stirring constantly so that they don’t clump or scramble.
Add ½ cup of the Parmesan cheese (you’ll reserve the other half to top the moussaka).
Add the salt and nutmeg and stir until everything is melted and combined. Turn off the heat.
Dry the eggplant slices with paper towels.
Drizzle olive oil into a large skillet and heat to medium-high.
Fry the dried eggplant slices, seasoned with salt and pepper on both sides, until lightly browned.
Once the potatoes are out of the oven, layer the fried eggplant slices on top.
Spoon the cooked meat sauce over the eggplant slices.
Spoon the bechamel sauce over the meat sauce.
Sprinkle the top with the remaining Parmesan cheese.
Bake, uncovered, for 1 hour.
Remove and allow to cool for 20 minutes before cutting into the moussaka. This will allow the moussaka to set up.