"Makes 4 servings. Ireland is known for wild-caught salmon. This recipe from the Bord Bia-Irish Food Board gives salmon a dinner party presentation. SEE MY NOTES BELOW - THIS RECIPE IS A WORK IN PROGRESS"
Place butter in a small bowl and beat in tarragon with the chives, garlic and a little salt and pepper to taste. Spoon onto a sheet of plastic wrap or nonstick parchment paper and shape into a roll about 1 inch thick, then wrap tightly. Chill in freezer at least 10 minutes to firm up (or keep in the fridge up to 48 hours until required, if time allows).
Cut the pastry into 8 even-size sections and roll each one out on a lightly floured surface into a 10- by 9-inch rectangle, trimming edges as necessary. Place a salmon fillet in center of each of four pastry rectangles. Unwrap the tarragon butter, cut into slices and arrange on top, then cover with the spinach leaves. Season spinach with salt and pepper to taste and add a little nutmeg.
Brush edges of pastry bases with a little of the beaten egg and lay a second sheet of pastry on top, pressing down to seal. Crimp edges by gently pressing the edge of the pastry with forefinger of one hand, between the first two fingers of the other hand. Continue all the way around the edge of the parcel, and then repeat until you have 4 parcels in total. Using a sharp knife, make light slashes across each parcel but take care not to cut through.
Place baking sheet in preheated oven for a few minutes. Meanwhile, brush pastry parcels with remaining beaten egg. Transfer to heated baking sheet and bake 25 to 30 minutes, or until pastry is cooked through and golden brown. Arrange salmon parcels on warmed serving plates. Serve with steamed green beans and hollandaise sauce, if desired.