Put the oven racks in the upper and lower thirds of the oven.
Arrange the eggplant on a large baking pan and brush both sides with oil.
Season with salt and pepper.
Bake until golden brown and tender, about 25 minutes.
Turn and rotate the slices half way through the cooking process.
FOR THE SAUCE:.
Whisk 1/4 cup of the milk, with the flour and garlic. Put in a saucepan and then gradually add the rest of the milk and 1/2 cup of the spaghetti sauce. Bring to a boil and reduce to a simmer. It should be pink. Cook until it thickens up. About 2-3 minutes should do it.
Spread the sauce on the bottom of a shallow 2 quart baking dish. Alternate the layers of the sauce and cooked eggplant.
Put the rest of the sauce on top, sprinkle with the cheeses and bake on upper rack until brown and bubbly. This should take 10-15 minutes.
I added some Italian bread crumbs on top of the cheese because I like how crunchy it gets.