In a stand mixer with a dough hook, combine dough ingredients except butter and cinnamon bits. Mix on medium-low for 7-10 minutes.
Add cold butter 1 to 2 tablespoons at a time, mixing until fully incorporated (8-12 minutes).
Add 1/4 cup cinnamon sweet bits and knead for 1-2 minutes.
Form dough into a ball, place in a greased bowl, cover, and let rise for 1 hour at room temp, then refrigerate for at least 3 hours.
Mix brown sugar, flour, cinnamon, salt, melted butter, water, and vanilla for the filling.
Line a 9-inch springform pan with parchment and grease the sides.
Divide dough in half, roll each to a 9x13-inch rectangle. Spread filling and remaining cinnamon bits evenly, then stack one piece of dough on top of the other.
Cut the stacked dough into 1 1/2-inch wide strips. Coil one strip in the center of the pan, and wrap the remaining strips around the coil.
Cover and let rise for 60-75 minutes. Preheat oven to 350°F.
Bake for 50-55 minutes, tenting with foil after 35 minutes. Bake until center reaches 190°F.
Combine glaze ingredients and drizzle over the warm cinnamon bun. Notes:
The dough must be chilled for at least 3 hours, but overnight is preferred for best flavor and handling.