Looking pretty but tasting very very bitter

We get more and more old vegetable varieties on the market.
A few weeks ago I bought these stunning baby aubergines. Not knowing what to do with them expect having them lying in avow and looking good I made a gratin with them. I probably should have tried them before going through all the effort … they were so bitter that one could not eat the dish.

Any one knows how to cook these little fellows?

Prettyaubergines  026-Edit

Prettyaubergines  008