6 tablespoons cold butter, unsalted
1/4 cup green onions, white and tender green parts only, thinly sliced
1 cup coarse fresh breadcrumbs
2 teaspoons fresh tarragon or 3/4 tsp dried, chopped
1 large egg, beaten
freshly ground black pepper
4 pieces tilapia fillets, about 6 ounces each
1/3 cup dry vermouth or dry sherry
1/3 cup chicken broth
2 teaspoons dijon mustard
1. Position a rack in upper third of over and pre-heat to 400F.
2. Melt 4 tablespoons of the butter in mediu saucepan or skillet over medium-low heat. Lightly brush the inside of a 9x13 pyrex baking dish with some of the melted butter. Transfer 1 Tbsp of the melted butter to a small dish and keep warm.
3. Add the scallions to the remaining butter and cook, stirring, until softened, about 2 minutes
4. In a medium bowl, mix the melted scallion butter with the breadcrumbs, tarragon, beaten egg, 1/4 tsp salt and several grinds of pepper.
5. Lightly season the fillets on both sides with salt and pepper. Lay a fillet on a work surface with the pointed end facing you. Mound a quarter of the stuffing on the pointed half of the fillet. Fold the wide split end of the fillet over and press firmly. (but don't squish) to cover the stuffing. Some stuffing will remain exposed. Put the stuffed fillets in the buttered baking dish. Brush the tops of the fillets with the reserved melted butter. Pour the vermouth and chicken broth around but not over the fillets.
6. Bake until the fish feels firm but flaky and the insides of the fillet look opaque with pierced with the tip of a sharp knife, about 20-25 minutes. Using a thin flexible slotted metal spatula, transfer the fillets to 4 dinner plates.
7. Add 1 tbsp cold butter to the hot baking dish and whisk until melted. Repeat with remaining Tbsp butter and mustard. Season sauce with salt and pepper and spoon over the fillets. Serve immediately.