Start by gathering all your ingredients. Add them all, except the butter, to the bowl of your stand mixer fitted with a dough hook. Mix on medium speed until the dough comes together. Cover, and autolyse/rest for 30 minutes.
550 g bread flour, 90 g sugar, 10 g salt, 1/2 tsp cinnamon, 1/8 tsp nutmeg, 250 g whole milk, 100 g eggs, 145 g sweet levain
Start your mixer again and knead on medium speed for about 10 minutes.
After 10 minutes, you want to slowly add cubed, softened butter, one cube at a time.
110 g unsalted butter
When you have added all the butter, continue kneading at medium speed for 15-25 minutes until your dough passes the window-pane test.
Place the dough in a clean bowl and proof in a warm spot, ideally at around 78°F/26°C, for two hours.
After two hours, transfer the dough to the fridge to cold-proof for a minimum of six hours.