Be careful not to overbake this veggie-loaded flat bread—the finished color should be a pale golden brown.
1. Combine 1 1/2 cups flour, yeast, sugar, and 1 1/2 cups room temperature water in bowl of stand mixer. Let stand 20 minutes. Add remaining 1 1/2 cups flour and salt, and beat on low speed with paddle attachment until dough comes together. (It should have consistency of thick pancake batter. If not, add up to 1/2 cup more water.) Add 2 Tbs. oil, increase speed to medium, and beat 15 minutes, or until dough becomes elastic and forms ball around paddle. Scrape dough from paddle, cover bowl, and let stand 2 1/2 to 3 hours, or until doubled in size.
2. Grease large, rimmed baking sheet with oil. Scoop dough onto prepared baking sheet, and sprinkle generously with flour. Press dough with hands to cover baking sheet. Cover, and let rise 1 hour.
3. Preheat oven to 450°F with oven rack in lowest position. Sprinkle dough with rosemary, then scatter with onion, artichokes, and sun-dried tomatoes. Dot with goat cheese, and sprinkle with kosher salt (if using). Drizzle with oil. 4. Bake 13 to 15 minutes, or until crust is browned around edges. Cool at least 20 minutes, then cut into 16 slices.