I first had a variation of this recipe at Serpico in Philadelphia and it was amazing. I've tried to recreate it at home ever since. This version combines sweet and flavorful monkfish medallions with a light dashi garnished with snow peas, radishes, and cucumbers. I cook the monkfish at 114°F (45.6°C) so it is lightly cooked but still not flaky. The dashi should be chilled so plan ahead for the time that takes. The fish will cool down once it's in the dashi, resulting in a fun cool and warm sensation as you eat it with the cold dashi.
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Preheat a water bath to 114°F (45.6°C).
Clean the monkfish and remove all membranes and connective tissue. Cut into 1" (25mm) medallions. Lightly salt and pepper the medallions then zest the lemon over the top. Place the monkfish in a sous vide bag with the butter then seal. Cook for 15 to 35 minutes, until heated through.
Remove some of the powdery coating from the kombu by gently wiping it with a damp cloth or paper towel. Add the kombu to a pot and cover with the water. Soak for 45 minutes.
Slowly heat the water to 160°F (71.1°C) over medium heat, this should take about 10 minutes. Remove the kombu from the pot and discard.
Turn the heat up to high and bring to a boil. Add the bonito flakes and remove from the heat. Let steep for 5 minutes. Strain the liquid to remove the bonito and any floating particles. Let the dashi cool and then place in the refrigerator to fully chill.
The dashi can be stored in the refrigerator for a week.
Remove the fish from the bag and pat dry. Briefly sear the medallions on one side.
Place the fish in the middle of a shallow bowl with the seared side up. Set some snow peas, radish slices and cucumber around the fish. Sprinkle some mint leaves on top of the fish. Pour the dashi around the fish. Drizzle some mirin and sesame oil in the dashi, squeeze a lemon wedge over the fish then serve.