Preheat oven to 350 degrees. Grease a bundt pan very well and set aside.
In a large bowl, whisk flour, both sugars, baking soda, baking powder, cinnamon and salt together. Beat in butter until mixture is crumbly. In a separate bowl or large measuring cup, whisk together eggs, vanilla, sour cream and milk. Make a well in the center of dry ingredients and pour wet in. Beat batter until light and fluffy, about 3 minutes.
Whisk filling ingredients together. Add half of batter to bundt pan and sprinkle filling on top. Swirl lightly with a knife. Add the rest of batter on top and swirl again, reaching down to the filling layer. Bake for 50-55 minutes or until a toothpick inserted in the enter comes out with a few moist crumbs. Do not over-bake! Upon removing cake from the oven, release the edges of the cake with a butter knife immediately. Allow cake to cool in pan for a few minutes before inverting onto a cooling rack to cool until slightly warm to the touch.
Whisk icing ingredients and drizzle on warm cake and sprinkle chopped pecans on top, optional.
Pecan Cinnamon Roll Bundt Cake will stay fresh for up to 5 days stored tightly in an airtight container at room temperature.