- In a bowl, combine the buttermilk, sugar, yeast and salt. Set aside.
- In a stand mixer using the dough hook or in a bowl using a wooden spoon, combine the flour, eggs and buttermilk mixture until the dough begins to form.
- Add the softened butter. In the stand mixer or by hand, knead the dough for 5 minutes. It will be soft and slightly sticky. Place in a clean, lightly oiled bowl and cover with a damp cloth or plastic wrap. Let rise in a warm, humid place for 1 hour.
- In a bowl, combine all the ingredients with a whisk until smooth. Pour into a buttered 13 x 9-inch (33 x 23 cm) glass baking dish. Set aside.
- In a bowl, combine the brown sugar and cinnamon. Set aside.
- On a generously floured surface, roll out the dough into a 20 x 14-inch (50 x 35 cm) rectangle. Brush with the melted butter and cover with the brown sugar mixture. Roll the dough into a log 20 inches (50 cm) long. Cut into 12 slices.
- Place the dough slices onto the caramel. Cover with a damp cloth or plastic wrap. Let rise in a warm, humid place for 1 hour, or refrigerate for 8 hours or overnight (see note).
- With the rack in the middle position, preheat the oven to 350°F (180°C).
- Brush the buns with buttermilk. Bake for 30 minutes or until golden brown. Let rest for 10 minutes.
- Place a large serving platter over the baking dish. Turn out the sticky buns onto the platter.