Sourdough starter:

Peel the potato and cut it into dice. Put them in a small saucepan with 1 cup (250ml) of cold water.

Bring to a boil, cover, and simmer for 20 minutes over low heat, until the potatoes are well softened.

Add 1/2 cup (125ml) of cold water from the tap. Blend with a mixer or food processor to obtain a thick liquid.

Let it cool down.

Pour the liquid potatoes into a large stainless steel or glass bowl and mix in the yeast and flour.

Cover the bowl loosely with plastic wrap.

Let it rest for 48 hours at room temperature. Stir occasionally; the sourdough starter is ready when it has a slightly sour smell and looks curdled.

The quantity obtained will be enough to make 2 large loaves. When the sourdough starter is ready, cover it with plastic wrap and refrigerate for up to 3 days, stirring occasionally.

Bread: Mix the sugar and water, and sprinkle the yeast on top. Set this mixture aside for 5 minutes. Then stir to completely dissolve the yeast.

Meanwhile, mix about 1 cup (250ml) of sourdough starter (half of the original mixture) and salt in the bowl of a stand mixer with a dough hook. Add 1 cup (150g) of flour, then the yeast mixture.

Start kneading the dough by adding flour gradually, as needed, to obtain a soft but well-formed dough (5 to 10 minutes). It may not be necessary to use all the flour.

Put the dough in a large, well-oiled bowl and turn the ball of dough in the bowl to coat it evenly with oil.

Cover the dough loosely with plastic wrap and let it rise for 50 to 60 minutes, or until it has doubled in volume.

(If you are baking later, cover it well and refrigerate for up to 1 day. In the refrigerator, the dough rises slowly. Deflate it from time to time.)

Place the dough on a lightly floured work surface. Lift the outer edges and fold them toward the center, pressing down to deflate the large air bubbles. Shape into a ball.

Divide the dough in two and place it in 2 greased 5×9-inch (13x23cm) loaf pans.

Sprinkle the top with a generous layer of flour. Cover loosely with plastic wrap. Let it rise for 30 to 40 minutes, or until the dough has doubled in volume. (Refrigerated dough takes about 1.5 hours to rise.)

Remove the plastic wrap and preheat the oven to 375°F (190°C).

Place the loaf pans in the middle of the oven and bake for 30 to 35 minutes.

By tapping the bottom of the pan, you get a hollow sound. Unmold and let cool on a wire rack. The bread is always better on the same day it was baked.