Mix all ingredients for the sourdough buns except the flour in a large bowl or in the bowl of a stand mixer. Add 2 1/2 cups of flour and mix in, then continue to add the flour, 1/4 cup at a time, until you have a smooth, supple dough. You may not need to add all of the flour, or you might need a little more.
Continue to knead for 4-5 minutes. Roll the dough into a smooth ball and place in an oiled bowl, turning over once to coat the top with oil. Cover tightly with a lid or cling wrap and let it rise overnight in a warm place.
The next morning, lightly grease two 8- or 9-inch cake pans. Prepare them by sprinkling the sugar for the glaze at the bottom of each, and then sprinkling the pecans atop the sugar.
Make the rest of the glaze by mixing the melted butter with the maple syrup and vanilla extract. Pour over the pecans and sugar in the cake pans.
Knead the dough lightly, lightly flour your work surface, then roll into a rectangle about 16 inches in length and 9 inches in width.
Make the filling by mixing together the cinnamon, nutmeg, and sugar. Spread it evenly on the dough you have rolled out, leaving a 1-inch border clear along one of the long sides of the rectangle.
Starting with the long edge covered by the sugar mixture, roll carefully into a log. Use a sharp or serrated knife to cut into 16 1-inch pieces lengthwise.
Arrange eight rolls in each of the cake pans. Cover the pans and let the rolls rise for 1-2 hours or until puffy and doubled. About 1/2 hour before baking, preheat the oven to 350 degrees Fahrenheit.
Place the buns in the oven and bake 30 minutes.
After removing from oven, let the buns stand five minutes, then invert carefully on a plate. Tuck in!