How to Make It
In a small bowl, whisk 1/2 cup of the warm water with the yeast. Let stand until foamy, about 5 minutes.
Meanwhile, sift the flour with the salt and sugar into a large bowl. Using your hands, pinch the 2 tablespoons of butter into the dry ingredients until it’s evenly distributed. Using a wooden spoon, stir in the yeast mixture and the remaining 1 1/2 cups of water until a shaggy dough forms. Scrape the dough out onto a lightly floured work surface and knead until smooth and elastic, about 10 minutes. Gently fold the dough under itself to form a ball and transfer to a large buttered bowl. Cover with a kitchen towel and let it rise in a warm place until doubled in bulk, about 1 hour.
Preheat the oven to 450°. Punch down the dough and scrape it onto a lightly floured work surface. Cut the dough into 4 pieces. Gently shape the dough into 4 rounds and transfer to a large baking sheet. Cover loosely with a kitchen towel and let stand in a warm place until nearly doubled in bulk, about 30 minutes.
Brush the rounds with the egg wash and sprinkle poppy seeds on top. Bake for 25 to 30 minutes, until well browned and firm. Let the loaves cool on the baking sheet for 20 minutes, then transfer to racks to cool completely. Slice the loaves and serve with crème fraîche.