Sift the 350 g flour into the bowl of a stand mixer fitted with the dough hook. Set the bowl aside.
Reserve 1 of the 4 eggs for glazing: put that egg aside refrigerated (you will use its yolk later). Crack the remaining 3 eggs into a small bowl and lightly beat them.
Warm the 50 ml milk gently until just warm to the touch (do not boil). In a separate small bowl, crumble the 10 g fresh yeast, add the 20 g sugar, pour in the warm milk, stir to dissolve, and leave for about 10 minutes until the mixture becomes slightly foamy.
Pour the 3 beaten eggs into the bowl with the sifted flour.
Start the mixer on low speed and slowly add the milk–yeast–sugar mixture to the flour and eggs. Continue mixing on low to form a rough dough, then increase to medium-low and knead for about 10 minutes until the dough is elastic and fairly smooth.
Cut the 200 g soft butter into small pieces. With the mixer running on low, add the butter pieces one at a time, waiting until each piece is fully incorporated before adding the next.
After all the butter has been added, knead the dough on medium-low for about 10 more minutes, until the dough is soft, elastic, and pulls away from the sides of the bowl.
Transfer the dough to a clean bowl, cover it, and leave it at a moderate room temperature until it doubles in volume.
Gently press the risen dough to deflate it, cover with cling film, and refrigerate for 12–24 hours.
The next day, remove the dough from the refrigerator. It will be firmer and easier to shape; let it sit briefly if needed to become workable.
Grease the baking pans well with butter and line the sides with baking paper so the paper extends about 10 cm above the rim.
Divide and shape the chilled dough into individual cupcake/brioche shapes and place them in the prepared pans.
Cover the shaped dough and leave to rise again at room temperature for about 2 hours, or until roughly doubled in volume.
Preheat the oven to 200 °C (390 °F). Separate the reserved egg: remove and beat the yolk (discard or reserve the white). Lightly brush the risen brioche with the beaten yolk and score the tops with a sharp knife if desired.
Bake at 200 °C for 15 minutes, then reduce the oven temperature to 170 °C (340 °F) and continue baking for another 30 minutes.
Remove the baked brioche from the oven and let cool in the pan for 5 minutes. Then lift the loaf out using the baking paper and leave the paper around it until it is completely cool. Enjoy.