Butter 4 shallow gratin dishes.

Melt 2 tablespoons butter in a large skillet over medium-high heat, then stir in leeks and 1 teaspoon salt, and cook until soft, stirring frequently 5 to 7 minutes.

Stir in anchovies and cook 1 minute, until the anchovies dissolve.

Add vermouth and bring to a boil, then let simmer until the wine evaporates almost completely. Remove from heat and scrape into a bowl.

In the same skillet, melt the remaining 4 tablespoons butter over medium heat. Whisk in flour and cook until pale golden, about 3 minutes. Slowly whisk in shrimp or seafood broth, and bring to a simmer, whisking constantly. Cook until very thick, then remove from heat.

Pat the fish cubes, shrimp and scallops dry. Stir them into the sauce along with the sautéed leeks, peas, tarragon, parsley, capers and remaining 1 teaspoon salt. Spoon mixture into prepared dishes.

Chill uncovered, for 1 hour.

In a small bowl, whisk together the egg with 1 teaspoon water. On a lightly floured surface, unroll pastry dough. Roll it 1/8-inch thick. Cut into 4 pieces to fit your gratin dishes (I cut mine into ovals). Place pastry on top of the pie but don’t seal the edges (it will stop the pastry from puffing). Brush the egg wash all over the pastry.

Place pies on a rimmed baking sheet and bake until the crust is golden about 25 minutes. Remove from oven and serve immediately.