Cook the potatoes (in their skins) in boiling water, until soft. Drain, and mash the first 5 ingredients. Set aside.
In a large, heavy skillet, saute the onions and garlic in 1 1/2 Tbsp of butter, with salt and pepper, until the onions are soft (5-8 minutes). Add the celery, mushrooms, and eggplant. Cook over low heat, stirring occasionally.
When the eggplant is cooked through (and this will happen more quickly if you cover the skillet between stirrings), add green pepper, herbs, and peas. Continue cooking about 5 minutes longer.
Remove from heat; toss with cheese, wheat germ, and vinegar. Spread this mixture into your buttered deep-dish casserole. Spread the mashed potatoes on top, as a crust.
OPTIONAL (and OPTIMAL): Sprinkle extra cheese plus some paprika on top.