Melt 6 tablespoons of the butter in a small saucepan. Take the pan off the heat and add 3 bay leaves. Let steep 1 hour. Remove bay leaves and discard.
Preheat oven to 350 (175 C) degrees. Coat a standard loaf pan with some butter. Dust the pan evenly with flour and line the bottom with a piece of parchment paper (easiest way to do this is to place the pan on the paper and trace all around the bottom edge with a pencil, use scissors to cut it out).
Dab one side of the remaining bay leaves in a bit of butter and lay them evenly along the bottom of the loaf pan, buttered side down.
Whisk the flour, sugar, baking powder and salt together in a large bowl.
Combine the eggs, crème fraiche, and melted butter in a medium bowl. Gently stir into the flour mixture just until the batter is smooth, without over-mixing.
Scrape batter into the pan carefully over the bay leaves. Put the remaining butter in a small zip-top bag and snip off one corner. Pipe the butter in a line down the center of the batter. Bake 45-50 minutes, until a toothpick inserted in the center comes out clean.
Remove from the oven and cool 10 minutes. Run a knife around the edge of the pan, then turn the cake out onto a rack to cool completely. Dust top with powdered sugar.