Julienne yellow onions and leeks, then sweat in butter until tender, season with salt and pepper, then cool and reserve.
Thinly slice potatoes lengthwise on a mandolin or slicer, soak in cold lemon water for at least 15 minutes to pull starch out. Thoroughly dry the potato slices, lay out overlapping and wrap around cod filet. Individually wrap potato cod in plastic wrap tightly.
Heat saute pan on medium-high heat. Add butter. While butter melts, remove cod from plastic wrap, then season generously with salt and pepper and place seam-side down in pan. Cook until golden brown, about 3-4 minutes, then flip over carefully and repeat. Remove from pan and reserve in a warm place.
In the same pan add garlic and asparagus, cook until heated. Deglaze with vermouth, reduce by half. Add heavy cream and reduce until thick.
In a shallow bowl or rimmed edge plate, lay down leek mixture. Plate potato cod over the top. Place asparagus at an angle on top and drizzle with cream sauce. Garnish with chopped Italian parsley and fresh grated lemon zest.
