1) Blend the biga ingredients until well combined. Cover the bowl, and let the biga rest, at cool room temperature, overnight. It will grow and become bubbly.
2) Mix all of the dough ingredients (including the biga), then knead for 3 to 4 minutes, using an electric mixer or bread machine. Or knead with your hands for about 5 minutes. Since this dough is going to ferment for quite awhile, you don't want to knead it fully; the gluten will continue to develop as the dough rises.
3) Place the dough in a bowl, cover it, and allow it to rise for about 3 hours. Once an hour, pick up the dough, gently deflate it, and return it to the bowl upside-down from how it was when you picked it up. This is called a turn; it helps distribute the yeast and yeast food.
4) Preheat your oven to 450°F, using a pizza stone if you have one.
5) Divide the dough into three pieces. Working with one piece at a time, roll the dough to a 1/8"-thick, 12" circle. Repeat with the remaining dough pieces. Ed. note: Jen says she rolls the dough on a floured work surface to about 8" in diameter, then picks it up, drapes it over her hands, and stretches it over the backs of her hands to about 12" — the way you would when making strudel.
6) Place the dough round on a cornmeal- or semolina-dusted piece of parchment, or onto a cornmeal- or semolina-dusted baking sheet. Allow the round to rise, covered, for about 20 minutes.
7) Brush the entire surface of the dough with olive oil, then spread about 1 1/2 cups grapes (about 10 1/2 ounces) over the dough, leaving a 1/2" border around the edge. Sprinkle the grapes with 2 to 3 tablespoons Sambuca or anisette; or with boiled cider, or grape juice. Place the bread in the oven (leaving it on the parchment if you're using a stone).
8) Bake the bread for 8 minutes, then remove the parchment, if the schiacciata is on a stone. Bake for an additional 4 to 7 minutes, until the schiaciatta is golden brown on the bottom and around the edges, and the topping is bubbly.
9) While the first bread is baking, prepare the second one.
10) When the first schiacciata is done, remove it from the oven, and place it on a rack to cool. Repeat the process with the remaining two schiacciatas.
11) Serve the schiacciata warm or at room temperature, cut in wedges, with a nice soft Brie or Saga blue cheese.
Yield: three 12" schiaciattas.