Preheat oven to 425 degrees. Roll out pastry on a floured surface to create 4 12x6 squares. Place 1 salmon fillet in the centre of each rectangle about 3 inches in from and parallel to 1 short edge.
Sprinkle each fillet with salt and pepper, 1 Tbsp of shallots and 1 tsp each of tarragon and dill. Brush edges of rectangles with some glaze. Fold long sides of pastry over fillets. Fold short edge of pastry over and roll up pastry to enclose fillets. Seal edges of pastry and place seam side down on baking sheet then brush the tops with glaze.
Bake pastries until dough is golden brown, about 20 minutes. Remove from oven and let stand for 10 minutes.
Meanwhile, boil wine, vinegar and 2 Tbsps of shallots in a saucepan until liquid is reduced to 6 Tbsps, about 8 minutes.
Remove pan from heat. Add butter 1 piece at a time whisking until melted before adding next piece.
Whisk in 2 Tsps of tarragon and then season sauce with salt and pepper. Spoon sauce over salmon wellingtons before serving.