Sourdough Starter

Mix together both flours. Measure 45 grams flour mixture (about 1/4 cup), setting the rest aside. Place in a bowl or container (we use a quart takeout container, so it's easy to watch grow). Add a scant 1/4 cup lukewarm water (45 grams) and mix until it creates a thick batter. Keep at room temperature, covered with a kitchen towel.

Repeat feedings of 45 grams each water and flour mixture once a day at the same time, mixing with a rubber spatula, for 4 days. In the beginning you won't notice much movement; by the end, the starter should appear lively, with a bubbly appearance.

On the 5th day, switch to entirely white flour and water, and start feeding twice—once in the morning and once at night. (At first you may smell some strong, not-very-pleasant smells, but eventually the starter will smell nutty and a little sour but pleasant.) Once it ferments—predictably rises, doubling in volume and creating a porous, webby-looking mixture after feedings—it is ready to use; this took us about 7 days. From this point, refrigerate your starter completely covered with the container lid.

Start a regular feeding schedule—at least once or twice a week. For each feed, to maintain a large starter, remove all but 100 grams (discard the rest, or use for another purpose, such as our banana bread and cookies recipe), and add 100 grams each all-purpose flour and water.

To maintain a smaller starter, remove 40 grams (discarding or using the rest), and feed with 40 grams each all-purpose flour and water. In the latter case, you may need to build your starter up to have amounts you'll need for recipes with leftover to maintain it; just feed without discarding for a couple of days in advance of when you'll need it.