Sourdough Focaccia with Onion and Sundried Tomato

Stir sourdough starter before measuring. Measure out 1-1/2 cups starter and bring to room temperature.Combine 2 cups flour and salt in a large mixer bowl. Gradually add water, olive oil and starter to flour mixture. Beat 2 minutes at medium speed of electric mixer, scraping bowl occasionally. Beat 2 minutes at high speed. Stir in enough remaining flour to make a soft dough. Knead on lightly floured surface until smooth and elastic, about 8 to 10 minutes. Cover; let rest 10 minutes.Roll dough to fit the bottom of lightly greased 15 x 10 inch jelly roll pan. Cover; let rise in warm, draft-free place until doubled in height, about 45 minutes.With handle of wooden spoon, make indentations in dough at 1-inch intervals. Top with Onion-Tomato Topping. Bake in preheated 450°F oven for 20 to 25 minutes or until done. Remove from pan; cool on wire rack.Onion-Tomato Topping: Heat oil over medium heat. Add onion; cook 4 to 5 minutes or until tender, stirring occasionally. Remove from heat; stir in salt, basil, thyme, pepper and tomatoes.