In a small to medium bowl, combine whole wheat flour, white flour, and salt. Crumble in the butter and mix until evenly distributed. In a separate bowl, whisk together lukewarm water, sugar, egg, and sourdough starter until fully combined.
Gradually add the dry ingredients to the wet and mix with your hands or a wooden spoon until a shaggy dough forms. Cover and rest for 1 hour.
After the rest, perform a set of stretch and folds to strengthen the dough. Cover and ferment until doubled — about 3–6 hours in a warm environment or 6–12 hours in a cool one.
In a small saucepan, melt the butter. In a separate bowl mix together the sugar, salt, and cinnamon. Combine with the melted butter to form a paste.
Spread ¼ cup of the cinnamon sugar paste over the bottom and sides of a glass baking dish. Sprinkle chopped pecans into the base and set aside.
Once doubled, turn the dough onto a lightly floured surface and knead lightly to build strength. Let rest under a bowl for 5–10 minutes. Roll out into a roughly 10x14 inch rectangle. Spread the remaining cinnamon sugar paste evenly over the dough and sprinkle with chopped pecans.
Roll the dough up tightly into a log and slice into 9 equal pieces approximately 1 inch wide. Place each bun cut side up in the prepared dish.
For long ferment: cover and refrigerate up to 24 hours, then rise in a warm spot for 2–3 hours until puffy and reaching the rim of the dish.For same-day: cover and rise in a warm spot for 2–3 hours until puffy and reaching the rim of the dish. Preheat oven to 375°F (190°C). Remove the cover and bake for 20–25 minutes until the tops are golden brown.
Let the buns cool for a couple of minutes. Place a cutting board over the dish and flip in one confident motion — the sticky glaze will pour down over the buns. Scrape any remaining glaze from the dish and spread it over the top. Cool for 15–30 minutes before serving.