Generously butter a 2 1/2- to 3-quart soufflé dish or six 1 1/2- to 2-cup soufflé dishes. If using small dishes, set them about 2 inches apart in a 10- by 15-inch baking pan.
In a 2- to 3-quart pan over medium heat, melt butter. Add flour and stir until mixture is smooth and bubbling. Stir in milk, tarragon, and salt, and continue stirring until sauce boils and thickens, 2 to 3 minutes. Add corn and dried tomatoes and stir until hot, about 1 minute. Remove from heat.
Add parmesan cheese and stir until melted. Add egg yolks and stir until mixture is blended and smooth.
In a bowl, with a mixer on high speed, beat egg whites (use whisk attachment if available) with cream of tartar until short, stiff, moist peaks form. With a flexible spatula, fold a third of the cheese sauce into whites until well blended. Add remaining sauce and gently fold in just until blended.
Scrape batter into prepared soufflé dish (or dishes). If higher than 3/4 full, use a foil collar (see "Crowning Glory" below). If desired, draw a circle on the surface of the soufflé batter with the tip of a knife, about 1 inch in from rim, to help an attractive crown form during baking.
Bake large soufflé in a 350° regular or 325° convection oven until top is golden to deep brown and cracks look fairly dry, 35 to 40 minutes. Bake small soufflés in a 375° regular or convection oven, 20 to 25 minutes. Serve immediately, scooping portions from single soufflé with a large spoon. Pass the shrimp-onion relish to spoon over each serving as desired.
Soufflés look most impressive when they rise dramatically over the rim of the dish. To create a beautiful crown on your soufflé, fill the dish about 3/4 full. If it's less full, the soufflé may not rise over the rim. If it's more full, the soufflé may spill over unless you wrap the dish with a foil collar. Here's how to make one.
Cut a 15-inch-wide sheet of foil 4 inches longer than circumference of dish; fold lengthwise in thirds. Coat one side of the foil strip generously with melted butter, using a pastry brush. Wrap the foil around outside of dish so that at least 2 inches of foil extend above the rim. Fold the ends of the buttered foil strip over several times until snug against dish.