Mix starter ingredients in small bowl and allow yeast to bloom until foamed, about 10 minutes. Milk should be warm, but not hot (~100F goal).
In mixer bowl with dough hook, add yeast starter with remaining ingredients for dough.
Combine and knead on medium speed until smooth, about 5 minutes.
Cover bowl with wrap and allow to rest to rise for 1 - 1 & ½ hours to double in volume.
While waiting, add peach filling ingredients in pan over medium heat and cook until peaches have softened completely and syrup thickens. Mash peaches lightly as it cooks.
Remove and cool slightly. Transfer to blender/food processor and pulse until smoothness desired. Set aside to cool completely.
Combine cream filling in bowl and whisk well until very smooth. Set aside.
After dough has double in volume, transfer to a lightly floured surface to roll.
Preheat oven to 350 F.
Roll out dough to a wide rectangle, about 10"x20". The dough about be fairly thin.
Carefully spread peach filling on dough, leaving a slight border around.
Do the same with the cream filling on top of the peach.
Roll as tightly as possible, leaving a 20" long roll. Brush the border with water to help seal completely.
Slice the roll immediately down the center, creating two half sphere rolls parallel to each other.
Pinch the far left sides of the two now cut rolls together.
Braid roll with alternating rolls. (If you need help visualizing this, search for braiding challah bread instructions.)
Press roll together if needed to fit into pan.
Carefully transfer to a greased and parchment strip lined loaf pan.