GETTING READY
1 Preheat the oven to 350°F.
2 Lightly oil a shallow, ovenproof dish.
3 In a large pot, heat plenty of salted water.
4 Trim off the ends of the eggplants.
5 Wash and dry them; cut lengthwise in half.
6 Scoop out the flesh, leaving a layer about 1/4 in thick next to the skin.
7 Add 2 tbsp wine vinegar to the boiling salted water.
8 Blanch the hollowed eggplants in it for 5 minutes.
9 Drain well.
10 On a clean cloth or tilted chopping board, arrange upside down.

MAKING
11 In a large nonstick skillet, heat 1/4 cup olive oil.
12 Fry the onion gently for about 10 minutes, stirring frequently.
13 When it is very tender and has started to brown, add the meat and fry for 1 minute, using a wooden spoon to prevent it from forming lumps as it cooks.
14 Add the chopped flesh scooped out of the eggplants.
15 Cook over low heat, stirring for 2-3 minutes.
16 Season with salt and freshly ground pepper, adding a pinch of chili powder if desired.
17 In a bowl, mix the garlic and parsley.
18 Stir into the meat mixture.
19 Add in the tomato sauce.
20 Keep stirring over low heat for 2 minutes to blend and thicken the mixture.
21 Remove from the heat and stir in the grated cheese.
22 Taste and correct the seasoning if necessary.
23 Fill the eggplant skins with the meat and vegetable mixture, smoothing the surface.
24 Arrange in the prepared ovenproof dish.
25 Bake in the oven for 30-35 minutes.
26 In a bowl, combine the béchamel sauce with the egg yolks and remaining grated cheese.
27 Return to a very low heat to cook, stirring gently, for a few seconds; do not allow to boil.

SERVING
28 On individual serving plates, arrange the baked eggplants.
29 Pass the sauce along.