Pour the water in a large bowl. Add the yeast and malt extract and stir to dissolve completely.
Add the rye flour, wheat flour, salt, and sourdough starter to the liquid mixture. Thoroughly mix everything together.
Knead by hand until smooth. Alternatively, knead in a stand mixer fitted with a dough hook for 3 minutes on low speed, then 4 minutes on high speed.
Place the dough on a floured countertop and cover with a kitchen towel. Allow to rise for 30 minutes, folding and kneading it every 10 minutes.
Gently form the dough into a round loaf and sprinkle with some flour.
With a sharp knife, cut a pattern into the surface, such as a cross, grid or square.
Put the loaf on a baking sheet, cover with a kitchen towel, and let it rise for another 30 minutes.
While the bread is rising, preheat the oven to 425°F/220°C.
Once the oven reaches the right temperature, take a spray bottle of water and spray the inside walls of the oven. Keeping the loaf on the baking sheet, transfer it to the hot oven.
Bake for 45 minutes, until a dark brown crust forms. Let cool before slicing and eating.