Prepare the sauce. Place the shallots and vinegar in a small saucepan. Boil until the vinegar has cooked away do not burn the shallots. Set aside.
In another saucepan, melt 2 tablespoons of the butter over medium heat. Whisk in the flour and continue whisking until the mixture is golden brown. Slowly add hot broth, whisking until thickened. Stir in the wine and the reserved shallots; continue cooking for 15 to 20 minutes. Strain the sauce into a clean saucepan and season with salt and pepper. Stir in the hot cream and the remaining tablespoon of butter.
Overlap the Tongue slices in a shallow baking dish and cover with the sauce. Bake in a preheated 350 degrees F oven until the top is golden brown, about 15 minutes. Serve immediately.