1 stick (1/2 cup) unsalted butter, softened
6 veal cutlets (scallopini; preferably cut from round; no more than 1/4 inch thick; 1 1/2 pounds total)
3 ounces Gruyère, coarsely grated (1 1/2 cups)
2 ounces baby spinach leaves (1 1/4 cups)
1/3 cup dry white wine
3 tablespoons finely chopped fresh flat-leaf parsley
Mash anchovy paste into 4 tablespoons butter in a bowl until combined. Gently pound cutlets to slightly less than 1/8 inch thick between 2 sheets of plastic wrap with flat side of a meat pounder or with a rolling pin. Pat cutlets dry and season lightly with salt and pepper, then spread 1 1/2 teaspoons anchovy butter over top of each cutlet. (You will have a little butter left over.) Sprinkle 1/4 cup cheese over anchovy butter, leaving a 1/4-inch border, then arrange spinach leaves, overlapping in 1 layer, to cover cutlets. Working with 1 cutlet at a time, arrange with a short side nearest you and roll up tightly, then secure with a wooden pick.
Put oven rack in middle position and preheat oven to 425°F.
Pat rolls dry. Heat 2 tablespoons butter in a 12-inch ovenproof heavy skillet over moderately high heat until foam subsides, then sauté veal, turning occasionally, until golden on all sides, about 4 minutes total. Transfer skillet to oven and bake veal until just cooked through, about 5 minutes. Transfer veal with tongs to a platter (reserve skillet) and keep warm, covered.
Pour off all but 1 tablespoon fat from skillet, then add wine and deglaze skillet by boiling (on stovetop) over high heat, scraping up brown bits, until reduced by half, about 2 minutes. Remove from heat, then add any juices accumulated on platter and swirl in remaining 2 tablespoons butter (not remaining anchovy butter). Cook over low heat until incorporated. Stir in parsley and salt and pepper to taste.