Went to 2* Bon Bon outside Brussels last week, guest chef was Ana Ros who is in charge of Hisa Franko in Slovenia and has hit the Worlds 50 best and won best female chef a couple of years back. I'm always a bit suspicious about these one offs as it is an unfamiliar kitchen and brigade and presumably a load of stuff needs to be shipped in. Tasting menu (no choice on the night) was a combination of her dishes and Hardiquest's (chef at Bon Bon):

Smoked eel, sweet sour cherry shisho condiment, puffed rice
Mackerel with Kriek Cantillon
Apricot, fermented cottage cheese, lily flowers
Tete de veau en tortue
Tripe cooked in wild game jus, fermented cheese, wild mushrooms, nettles
Haddock and lobster, ginger mousseline
Bear, trout, honey, berries
Peach, sweetwoodruff milk, local saffron
Smoked white chocolate, red beet tartar, puffed rice

This was, until the end, a solid 1.5 to 2 star meal for me. Wine pairing was serviceable but didn't make any of us go "ooh what on earth is that" at any point. The tripe dish was by far the best tripe dish I've ever had, cut through with cheese it was delicious and was the dish of the night and I don't even really like tripe. The mackerel, cottage cheese and tete de veau were up there as well. Unfortunately it all fell apart at the end when they ran out of smoked white chocolate and served us a beetroot salad as our final dessert, which at that stage with no sweetness was a disaster. I wondered about this, surely it would have been better not to serve it as at all and either replace (maybe they couldn't because they didn't have anything else or because they were already cleaning down the kitchen) or make some other concession. We also missed out on mignardise which other tables were served and then had an extra dinner added to the bill which had to be sorted out.

It was a shame because it was good until then and the menu as a whole was well balanced and fun to eat...but ending like that really made the €400 bill stick in the throat. Noone there seemed to particularly care that we'd had a substandard experience relative to the other diners and I guess that's what really did the damage. A shame and more grist to the mill for my suspicions regarding these one off guest chef affairs.