1 Reserve 2 tablespoons milk and heat remaining milk until luekwarm. Crumble yeast into milk and stir until it has dissolved. Rinse lemon in hot water, wipe dry and finely grate 1 teaspoon zest.
2 Separate 3 eggs. In a bowl, beat the softened butter with egg yolks, maple syrup and 1 pinch of salt until frothy. (Reserve egg whites for another use.)
3 Stir lemon zest into butter mixture.
4 Alternately stir the yeast mixture and flour into butter mixture, then knead briefly.
5 Turn out dough onto a lightly floured work surface and knead. Place in a bowl and let rise in a cool place or in the refrigerator until doubled in bulk, about 8 hours.
6 Meanwhile, chop the nuts.
7 Combine the nuts with the dough. Let dough rise for about 30 minutes.
8 Divide the dough into thirds on floured surface and roll into ropes, about 40 cm (approximately 16 inches) longs.
9 Braid the dough ropes and carefully place on a plate lined with parchment paper.
10 Separate the remaining egg. Beat the egg yolk with some of the reserved milk and brush the brioche dough with it. (Reserve egg white for another use.)
11 Place the brioche in a cold oven. Heat to 200°C (fan 180°C, gas: mark 3) (approximately 350°F) and bake until golden brown, 45-50 minutes. Let cool on a cooling rack before serving.