Stir sourdough starter before measuring out 1 C.. Bring that 1-C. portion to room temperature. In a large bowl, combine 2/3 C. flour, undissolved yeast, salt, basil and oregano. Heat water and 2 Tbs. of the olive oil until very warm (120-130 degrees). Gradually add water mixture and starter to the flour mixture. Beat 2 minutes at medium speed of electric mixer, scraping bowl occasionally. 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 a 13- by 9-inch rectangle. Press evenly into a greased 13-by-9-inch baking pan. Cover; let rise in a warm, draft-free place until almost doubled in size, about 30 minutes. With handle of a spoon, make an indentation in dough at 1 1/2-inch intervals. Brush dough with olive oil and sprinkle lightly with coarse salt. Sprinkle with olives and mushrooms. Bake at 400 degrees for 30 minutes. Serve warm.

Yield: One (9-by-13-inch) flatbread, or 6 servings.