Step 1Bring water to boil in a medium saucepan. Blanch the fennel greens for about 15 to 20 seconds, then remove and drain.
Step 2Puree the fennel fronds in a blender with the garlic, then drizzle the olive oil into the blender with the salt and add lemon juice to taste.
Step 1Put 4 cups water, the wine, peppercorns, bay leaf and lemon zest in a large saucepan (big enough to hold the 4 fillets) and bring to a boil. Reduce the heat to medium and simmer for 5 minutes for the flavors to steep.
Step 2Using a spatula, lower the fillets into the hot liquid and poach for several minutes just until stiffened (if there is not quite enough liquid to completely cover the fillets, add equal parts wine and water to cover). Remove the fillets from the liquid, drain and place on warm serving plates.
Step 3Ladle 2 tablespoons fennel sauce on each fillet and sprinkle 2 to 3 drops of colatura on each fillet, or to taste.