Brioche is a rich and “heavy” dough, and for perfect raising, it is very important to properly prepare the leaven. For this, take 20 g of “ripe” sourdough starter at its peak and mix: 20 g of sourdough starter + 10 g of water + 20 g of flour. Get 50 g of sourdough. Put it in a warm place and wait until it ferments and is at its peak (it will increase 2-3 times). Then mix again: 50 g of sourdough starter + 25 g of water + 50 g of flour. Get 125 g of fermented sourdough starter. Then take from there 120 g of sourdough and mix: 120 g of sourdough + 120 g of water + 60 g of flour. This will give 300 g of “ripe” sourdough, thick sourdough starter for the recipe. Wait until it ferments and is at its peak (it will increase 2-3 times) and use it for the recipe. If you are confident in the strength of your sourdough starter and it does not sour, you can use it without preliminary preparation, but brioche is a kind of bread that contains more sourdough than flour, therefore, if the sourdough is sour, then the brioche will also be sour.
When brioche is baking, the dough grows very quickly. Correctly fermented dough forms a beautiful dome. If the dough is not fully fermented, it will crack during baking. To avoid this situation, you can make several cuts on the surface with a razor or scissors.
We bake brioche in the tin loaf. But you can use this dough to make a Parisian brioche (with a "head", as in the paintings of E. Manet), brioches for burgers and brioches of any other shape you like.