Potatoes

Two very different roles

As a topping, thin potato slices bake into a crisp-edged, tender lid that is one of the most satisfying focaccia toppings — think potato-rosemary focaccia. Worked into the dough, cooked potato adds moisture and starch that give an exceptionally soft, pillowy, long-keeping crumb, a trick used in focaccia barese and some regional breads.

They are unrelated techniques that happen to share an ingredient, so decide which effect you want first.

Potato as a topping

The critical rule: slice thin. A hot focaccia bakes in 20–30 minutes, not long enough to cook thick raw potato through, so slabs come out hard and starchy. Slice to a couple of millimeters — a mandoline gives even, translucent slices — and toss them in oil so they cook and crisp rather than dry into chips.

Lay the oiled slices in overlapping tiles, season with salt and rosemary, and press lightly so they adhere. They will turn tender with golden, crisp edges by the time the bread is done.

Potato in the dough

Boil a floury potato until soft, mash or rice it smooth, cool it, and work it into the dough (recipes give the proportion). The extra starch holds water, so the crumb stays soft and moist for longer and takes on a subtle sweetness. Because potato adds moisture, you may need to adjust the added water.

Use a plain boiled potato with no butter or salt added unless the recipe accounts for it.

Which potatoes and how to store

For crisp toppings, waxy or all-purpose potatoes hold their slices well; for dough, floury (starchy) potatoes mash smoothest and add the most softness. Store potatoes somewhere cool, dark, and airy — not the fridge, which turns their starch sweet — and away from onions, which speed each other’s spoiling. Discard any green or heavily sprouted ones.