Scald the milk in a small pan and let cool until tepid. Crumble or sprinkle the yeast on top and leave until dissolved, about 5 minutes. Sift the flour onto a work surface with the salt and sugar and make a large well in the center. Add the eggs and yeast mixture and work lightly with your hand until mixed. Using a pastry scraper or spatula, gradually draw in the flour, working the mixture until it forms large crumbs. Press it into a ball; the dough should be soft and slightly sticky; if necessary add more flour.

Flour the work surface and knead the dough until it is smooth and elastic, at least 5 minutes. Work in the creamed butter and continue kneading until the dough is smooth again, 2-3 minutes. Shape the dough into a ball, transfer it to an oiled bowl and leave to rise in a warm place until doubled in bulk,

1-1/2 hours.

Butter a baking sheet. Turn the dough on to a lightly floured surface and knead lightly to knock out the air. Roll it to the largest possible round that will fit the baking sheet, preferably 50 cm across. Transfer the dough round to the buttered baking sheet and with your knuckles, flatten the center slightly to form a 1 inch//2.5 cm border around the edge to contain the butter and sugar topping. Dot the top with butter. Mix the lemon zest with the sugar and sprinkle it on the dough. Leave the galette in a warm place to rise until light, 15-20 minutes. Heat the oven to 450 F//230 C.

Bake the galette in the heated oven until browned and the sufar has formed a crisp glaze on top, 15-20 minutes. Transfer it to a rack to cool. It is best served while still warm, but can be baked a few hours ahead and warmed for serving. Serves 6-8.