As others have said, the chances are you'll be doing a D-gate to D-gate transfer. I guess you'll be on the 'early' mornign flights (dep. AMS 09:20?), so you probably won't appreciate Murphy's Irish Bar (in the D-gate zone itself - useful if you're a smoker) () but there are quite a few shops and snack bars around.

55 mins is plenty of time! But, even if your inbound is late, and you land on the Polderbaan (the far-western runway, which is a 15-20 minute taxi to the gate/stand), and you arrive at the bus gate (D6, I believe, which will be the case if your flight is operated by KLM Cityhopper), and there's some sort of commotion preventing you from getting your onward flight ... Don't Panic!

... IIRC, there's at least one more KLM flight to Bucharest later on and at least one daily Tarom flight ... KLM will move you to one of these for free (and, maybe, even give you some compensation vouchers) if you miss your connexion!

Bon Voyage!

-- Henry