Past dry the fish. Sprinkle with salt and pepper. Place a large sheet of parchment on work surface. Halve each potato lengthwise. Using a mandolin, slice each potato half very thinly. Set 5 to 6 slices on parchment in a row, overlapping long sides. Set 5 to 6 slices of potatoes overlapping going on the opposite direction, forming a 6x5 rectangle. Sprinkle the rectangle with salt and pepper. Set 1 fillet across overlapped short end of slices.
Fold sides of rectangle over fish, forming packet. Press to adhere. Sprinkle with salt and pepper. Repeat with remaining potato slices and fish fillet.
Heat 1 tablespoon oil in a large skillet over medium-high heat. Set wrapped fish fillets, seam side down in the skillet. Cook until golden on bottom, about 6 minutes. Turn and cook until the fish is opaque in the center, 4 to 5 minutes longer. Transfer to plates, cover and keep warm.
Add 3 tablespoons of oil to skillet and add the garlic and shallot. Stir for 1 minute. Add wine and saffron. Cook on high heat for 30 seconds. Add the cream and reduce by one half. Season with salt and pepper. Add the mascarpone and remove from the heat. Spoon sauce over the prepared sea bass fillets and serve.