Combine the active sourdough starter, cold milk, bread flour, and sugar in a bowl. Stir until mixed. Cover and allow to rest in a warm place for 4 hours.

Gather all the ingredients. In the bowl of a stand mixer fitted with a dough hook, combine the bread flour, sugar, salt, cinnamon, nutmeg, cold milk, eggs, and sweet levain. Mix on medium speed until a dough forms. Cover the bowl and let it rest for 30 minutes.

Resume mixing on medium speed for about 10 minutes.

Gradually add the softened butter, one cube at a time, to the dough.

Once all the butter is incorporated, continue kneading on medium speed for 15-25 minutes, or until the dough passes the window-pane test.

Transfer the dough to a clean bowl and allow it to proof in a warm place (around 78°F/26°C) for two hours.

After the initial proof, move the dough to the fridge to cold-proof for at least six hours.

In a bowl, mix the softened butter, white sugar, dark brown sugar, and cinnamon with a fork until a spreadable paste forms. Keep at room temperature until ready to use.

In a small pot, combine the unsalted butter, dark brown sugar, and maple syrup or honey. Bring the mixture to a simmer while stirring. Once everything is melted and combined, remove from heat and add salt to taste.

Lightly toast the pecans in a dry pan over medium heat for a few minutes.

Pour the caramel glaze into the bottom of a 13×10 baking pan and sprinkle with the pecans (chopped if desired). Allow the mixture to cool for 10-15 minutes.

Place the dough on a lightly floured surface.

Roll the dough into a 19x12in/50x30cm rectangle using a rolling pin.

Spread the cinnamon filling evenly over the dough.

Starting from the long side, tightly roll up the dough. Trim the edges, then cut the roll into 1.5-inch/4 cm pieces using a sharp knife or floss, yielding 12 buns.

Arrange the buns in the prepared 13×10-inch/25x34cm baking pan, on top of the caramel and pecans.

Cover the pan with plastic wrap and let the buns proof at around 78°F/26°C for 9-12 hours, or until doubled in size.

Preheat the oven to 355°F/180°C.

Bake the sticky buns for 18-20 minutes until golden brown. Allow to cool for 10 minutes, then invert the buns onto a serving tray to reveal the caramel-pecan topping.