Crumble yeast for the dough. Mix with 1 tablespoon of sugar. Mix flour and 1 teaspoon salt. Add yeast, about 350 ml lukewarm water and oil. Knead to a smooth dough. Let dough rise for about 1 hour.
For the garlic butter peel the garlic and chop it very finely. Wash the herbs, shake dry. Pluck off leaves or needles and chop finely. Cream 100 g butter. Stir in garlic and herbs.
Coarsely grate both cheeses.
Briefly knead the yeast dough on a floured work surface. Roll out to a square (approx. 50 x 50 cm) and spread with garlic butter. Sprinkle cheese evenly on top. Cut into 6 strips.
Place 3 strips on top of each other, placing the top strip with the butter side down. Cut both dough stacks crosswise into 6 pieces each.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Grease a box mould (25-30 cm long; approx. 1 3⁄4 l capacity). Place vertically. Layer pieces of dough in the mould.
Sprinkle with fleur de sel. Cover and leave to rise for about 30 minutes. Bake in a hot oven for 35-40 minutes. Remove from the oven and leave to cool for about 15 minutes. Then carefully turn out of the tin.