Take the well-bubbling starter out of the fridge.

Sift both types of flour into a bowl, pour in the cold water and quickly knead the dough by hand. Cover with plastic wrap and leave for an hour in a warm place - this is the autolyse.

Add the active starter, salt and sugar and knead into a more even, tender dough; if needed, add a couple more tablespoons of flour.

Leave the dough in a warm place for an hour, then fold it and let it rest for another 30 minutes.

Turn the dough out onto a floured surface, divide into three pieces and shape into baguettes: stretch each piece into a rectangle, then fold the edges to the center, pinching them closed, until stretched into shape.

Transfer the baguettes to a parchment-lined baking sheet, pleating the parchment between them, cover with a towel and leave in a warm spot for 1.5-2 hours until they expand.

Place a baking stone on the middle rack of the oven, set a pan below it, pour in a cup of boiling water and preheat the oven to 240-250 °C.

Score the baguettes, mist them well with a spray bottle and bake with steam on the stone for 15 minutes.

Remove the pan of water, lower the oven to 210 °C and bake for another 15 minutes.

Let the finished baguettes cool completely before tasting.