In a bowl, mix the buttermilk and sugar. Set aside.

In another bowl or a stand mixer (with the dough hook), mix the flour, yeast, and salt. Add the buttermilk mixture and mix vigorously until the dough starts to form.

Gradually incorporate the butter and knead the dough for about 5 minutes in the stand mixer or on a floured surface. The dough will be soft and slightly sticky. Place the dough in a clean, lightly oiled bowl. Cover with a damp cloth and let rise in a warm, humid place for about 1 hour.

Generously butter a Bundt pan. Set aside.

In one bowl, pour the melted butter. In another bowl, mix the brown sugar, sugar, and cinnamon. Set aside.

Remove the dough from the bowl and cut it into approximately 40 pieces of varying sizes. Without overworking the dough, shape into balls using your palms.

Dip the dough balls in the butter to coat well. Roll in the brown sugar mixture and place them in the prepared Bundt pan. Pour any remaining brown sugar mixture and butter over the dough balls in the pan. Cover with plastic wrap and let rise in a warm, humid place for 45 minutes.

Place the oven rack in the center. Preheat the oven to 180°C (350°F).

Remove the plastic wrap and bake for 40 minutes for a dark pan or 45 minutes for a light pan, or until the caramel is golden brown and bubbling at the edges. Immediately invert onto a serving plate. Let cool for 15 minutes before serving. Best enjoyed warm or cold the same day.