This is similar to the Multigrain Sandwich Bread in Chapter 5, but it’s made with sourdough rather than the quick-fermenting sponge in that recipe. Thanks to Tim Healea of little t american baker in Portland, Oregon, for sharing his recipe.
For the levain, stir the water and sourdough starter together in a medium bowl. Stir in the flour. Cover the bowl with clingfilm and let the sponge ferment 8-12 hours, until bubbly. If it’s warm in the kitchen, it will be ready after only 8 hours.
For the dough, stir the water and the levain together in the bowl of an electric mixer and stir in th