In a bowl in the microwave, melt your butter for the dough. Add the milk and continue heating the mixture until warm. Stir in the active dry yeast and 1 teaspoon of granulated sugar and allow to sit for 5-10 minutes, or until the mixture is frothy. In a large bowl, stir together all the dry ingredients for the dough (flour, sugar, and cinnamon). Pour in the yeast mixture and knead until no longer sticky. Allow to rise in a warm place in a greased bowl for about an hour, or until double in size.
To make the vanilla pudding filling, heat the heavy cream over low-medium heat in a small saucepan. Cut your vanilla bean in half and scrape out the seeds into the cream. In a large bowl, whisk together your egg yolks, cornstarch, and granulated sugar. Pour the hot cream into your bowl, and whisk until completely lump free. Pour the mixture back into your saucepan and continue heating until thick (5-8 minutes). Transfer the pudding to a bowl, whisk in the vanilla extract, and allow to cool completely.
Wash and dice your nectarines into small pieces. Transfer your diced nectarines to a small saucepan, stir in the granulated sugar (the amount depends on how sweet your nectarines are) and cornstarch, and cook over medium heat until tender.
Roll your dough into a rectangle on a lightly floured surface until it’s about 1/3″ thick. Use your fingers to create two shallow lines down the length of the dough so you have 3 equal sections. Fill the middle section with your vanilla cream (you’ll probably have more than your able to use so be careful not to overfill!) and nectarines leaving an inch of space at either end. Cut the outer sections into inch wide strips. Fold the top and bottome over the filling, and begin braiding the loaf by crossing your outer strips over the middle alternating from side to side.
Allow the dough to rise another half an hour before baking at 410F/210C for 20-25 minutes, or until golden brown.