Dot's second course

Back of cod with citrus fruit roasted in olive oil, quinoa risotto with lemon, white butter sauce emulsified. The quinoa was hiding under the foam. They serve foam with a lot of dishes here in France. What's with the foam? They also gave her a weird looking butter knife with a notch in it. Wasn't sure what she was supposed to do with it. We were afraid there might be bones in the fish, but nope.