Preheat oven to 350 degrees F. Butter and flour 9 inch cake round.
For topping, melt butter and set aside. In a separate bowl mix sugars, nutmeg and salt then add melted butter and mix well. Add flour and mix until it comes together and crumbles. Set aside.
For cake: Place sugar and butter in a stand mixer and mix at high speed for about five minutes until mixture is fluffy and turns white. Meanwhile sift dry ingredients in a separate bowl and set aside. Scrape bottom of mixing bowl to ensure butter and sugar are well incorporated. Reduce speed to low and add eggs one at a time combining well and then add vanilla and sour cream. Add flour mixture on low speed and mix until Just combined.
Combine 3 Tbs of sugar and 1 tsp of cinnamon in a small bowl and mix.
Pour half batter into prepared pan and sprinkle a generous amount of the sugar-cinnamon mixture all over then pour remaining batter. Top with crumble until its completely covered. Bake for 25-35 minutes depending on your oven.
To make glaze: Place sugar, butter, buttermilk and cornstarch in a small sauce pan on medium heat. Stirring constantly bring mixture to a boil. Cook for about one minute until slightly thickened. Remove from heat add vanilla, salt and baking soda.
Once the cake is done, set it aside to cool enough to handle and remove from pan. Add glaze while cake somewhat still warm. Enjoy!