Add the active sourdough starter, milk, flour, eggs, salt, sugar, and vanilla extract to the bowl of a stand mixer fitted with the dough hook attachment.

Mix on low to medium speed until a shaggy dough forms.

With the mixer running, add the softened butter one tablespoon at a time, allowing each addition to incorporate before adding the next. Scrape down the sides of the bowl as needed.

Resist the urge to add extra flour unless absolutely necessary. Brioche dough should be soft and slightly sticky, and adding too much flour can result in dense, dry sticky buns.

Brioche dough can rise slowly. In a cooler home, around 68°F, the first rise may take closer to 10 hours. Watch the dough rather than the clock.

Add the brown sugar, heavy cream, butter, and salt, if using, to a medium saucepan over medium heat.

Whisk for 5–8 minutes, allowing the mixture to bubble and thicken.

Once the caramel has thickened, add the vanilla extract and continue cooking for another 1–2 minutes.

Pour the warm caramel into the bottom of a greased 9×13-inch baking dish. Sprinkle the chopped pecans evenly over the caramel.

Once the dough has risen, turn it out onto a lightly floured surface.

Roll the dough into a 12×18-inch rectangle, approximately 1/4-inch thick.

Spread the softened butter evenly over the surface of the dough. Sprinkle the brown sugar evenly over the butter, followed by the cinnamon.

Use a pizza cutter or pastry wheel to slice the rectangle in half, then in half again, and then in half once more, creating 8 even strips.

Roll each strip into a spiral and place the rolls cut-side up over the caramel and pecans in the prepared 9×13-inch baking dish.

Cover the baking dish and let the sticky buns rise at room temperature for 1–3 hours, or until they are puffy and visibly risen.

Preheat the oven to 350°F (175°C).

Bake the sticky buns for about 35 minutes, or until golden brown and the internal temperature reaches at least 195–200°F (90–93°C).

Allow the sticky buns to cool for a few minutes before carefully inverting the baking dish onto a large serving platter or baking sheet. The warm caramel and pecans will coat the tops of the sticky buns as they are turned out.

Serve warm.