Preheat the broiler and position an oven rack 8 inches from the heat.
Prepare asparagus by holding asparagus spear in your hand and breaking off the bottom where it snaps; this is the tough part of the stem. Discard.
Melt butter in a large sauté pan. Add minced shallots and cook over moderately high heat until softened, about 1 minute. Add prepared asparagus, season with salt and pepper, and cook briefly over moderate heat, stirring occasionally, until crisp-tender.
Transfer asparagus to a medium gratin dish and arrange with asparagus heads pointing in once direction.
Combine crème fraiche and grated gruyere cheese. Spread evenly over asparagus. When ready to serve, broil until golden and bubbling, shifting the dish for even browning, about 1-3 minutes. Sprinkle with tarragon and serve.