Shuck oysters. Reseve liquid (oyster liquor) for cooking, and the shells for serving.
Pour oyster liquor and sake into saute pan. Cook over medium heat for 5 minutes and the mixture becomes frothy. Add butter to the pan. Whisk until butter is melted. Add oysters and poach for 2 minutes or until edges begin to curl.
Return oysters to shells. Serve with 1 teaspoon of poaching liquid. Garnish with pickled shallot and tobiko.