An enriched French brioche with a soft, tender crumb and rich buttery flavor, shaped as a lofty Brioche Nanterre for pillowy, flaky slices perfect on their own or for indulgent toast and sandwiches.
Whisk the dry ingredients (bread flour, yeast, sugar, salt) together in the bowl of a stand mixer fitted with a dough hook.
Add the cold whole milk and cold eggs; mix on medium-low until a shaggy dough forms, stopping to scrape the bowl as needed.
Increase to medium speed and knead 8–10 minutes until the dough is smooth and begins wrapping the hook and slapping the sides; if not, add a little flour 1 Tbsp at a time until it does.
Plasticize the butter: place the cold butter between 2 sheets of parchment and pound with a rolling pin until very thin (about 1/16 inch/1.6 mm). Keep cold.
With the mixer on medium-low, add the cold butter 2 pieces at a time, letting each addition fully incorporate before adding more; scrape the bowl as needed. Mix a couple more minutes until the dough is very smooth, shiny, and elastic.
Shape the dough into a ball, place in a greased bowl, cover tightly, and refrigerate overnight for at least 12 hours and up to 48 hours.
Grease a loaf pan. Turn the cold dough out, divide into 6 equal pieces, and shape each into a tight ball (smooth top, sealed bottom).
Arrange the 6 balls in the pan (Brioche Nanterre style), cover, and let rise at room temperature until the dough just reaches the top of the pan, about 1½–2 hours (longer if cool).
Brush the top with egg wash.
Bake until deep golden and cooked through, about 35–40 minutes; tent loosely with foil halfway through to prevent over-browning.
Cool in the pan 10 minutes, then transfer to a wire rack and cool at least 1 hour before slicing.