While the fish is cooking, make the sauce. Put the egg yolk and lemon juice in a small lidded jar. Shake well, until emulsified. Melt the butter in a small pot, then pour into the jar. Cover ...
Stir in the mascarpone and butter. Add the kale, and lemon zest and juice to taste ... about 3 to 5 minutes. Transfer the pasta to the sauce, finish with Parmesan, and toss to coat.