Preheat oven to 450 degrees. Heat 1 cup Sake in a small saucepan over medium heat. Slice the ginger into 1/4 slices and then bruise the slices with the handle of the knife. Add the sliced ginger and minced shallots to the Sake and reduce to 1/8 cup. Remove from the heat and slowly whisk in the butter. Strain the liquid through a chinoise and keep warm. While the Sake is reducing, wilt the spinach in a sauté pan with a tablespoon of Sake and 1/2 tsp. of sesame oil. Remove the oysters from the shells and wrap them in spinach, then proscuitto and then place back in the shell. Place the oysters on a small baking pan and broil for 6-10 minutes until the proscuitto starts to crisp. Serves 2 as an appetizer. (Oysters may also be browned in a sauté pan)