Adjust oven rack to middle position and heat oven to 400 degrees. Grease 1 1/2-quart soufflé dish or 8-inch-square baking dish. Whisk cornmeal and 3/4 cup milk in bowl until combined; set aside.

Melt butter in Dutch oven over medium-high heat. Cook corn until beginning to brown, about 3 minutes. Stir in remaining milk, sugar, salt, and cayenne and bring to boil. Remove from heat, cover, and let mixture steep 15 minutes.

Transfer warm corn mixture to blender or food processor and puree until smooth. Return corn mixture to pot and bring to boil. Reduce heat to low and add cornmeal mixture, whisking constantly, until thickened, 2 to 3 minutes; transfer to large bowl and cool to room temperature, about 20 minutes. Once mixture is cool, whisk in egg yolks until combined.

With electric mixer on medium-low speed, beat egg whites and cream of tartar until frothy, about 1 minute. Increase speed to medium-high and beat until stiff peaks form, about 3 minutes. Whisk one-third of whites into corn mixture, then gently fold in remaining whites until combined. Scrape mixture into prepared dish and transfer to oven. Reduce oven temperature to 350 degrees and bake until spoonbread is golden brown and risen above rim of dish, about 45 minutes. Serve immediately.