In the bowl of a stand mixer, combine the all-purpose and whole wheat flours. In a separate bowl, whisk together the milk, egg, and sourdough starter until the mixture is smooth. Using the dough hook, start the mixer on speed 2 and slowly incorporate the liquid mixture into the dry ingredients. Increase to the next speed briefly once the flour is mostly absorbed to knead for 30 seconds. Let rest for 15 minutes.

Resume mixing on speed 2, adding sugar, salt, and one piece of butter at a time, ensuring each piece is integrated before adding the next. Once all butter is added, increase to speed 4 and knead for 8 minutes until the dough is cohesive, glossy, and pulls from the sides, while remaining tacky.

Transfer the dough to a bowl, cover it with a damp cloth or seal inside a large plastic bag. Allow to ferment overnight at room temperature (approximately 68–70°F) until it doubles in size and becomes airy—typically 10 hours.

The next morning, gently turn the dough onto a generously floured surface. Pat into a rectangle and cover with a linen towel. Begin the caramel by melting the butter in a saucepan. Stir in the brown sugar, honey, salt, and cream. Bring to a boil, whisking constantly. Reduce to a simmer for 5 minutes until thick and glossy. Pour into a 9×13-inch baking pan and sprinkle pecans over the top. Chill the pan on a rack in the refrigerator for 15–20 minutes.

Roll the dough into a 16" x 12" rectangle using a floured pin. Brush melted butter over the surface, leaving a ½-inch margin along the edges. Combine the brown sugar, cinnamon, and salt, and distribute evenly over the buttered dough.

With a bench scraper and floured hands, roll the dough tightly from the long edge into a log, pinching the seam to seal. Slice the log into roughly 2½-inch segments and place cut-side up in the caramel-coated pan.

Cover the pan with a clean bag or cloth and leave to proof for around 3 hours in a warm area until the rolls expand and touch.

Preheat oven to 375°F. Bake for 30–35 minutes until golden and firm in the center. Check for an internal temperature of 205°F if desired.

Let the pan rest for 5 minutes. Place a piece of parchment larger than the pan over the rolls, then a baking sheet on top. Invert the pan using oven mitts and remove the baking dish carefully. Allow any residual caramel to drip onto the buns.