5tablespoonscold unsalted buttercut into small pieces
1 1/2cupspowdered sugar
3 to 4tablespoonseggnog
Preheat the oven to 350 degrees F. Coat a 9 or 10 inch springform pan with cooking spray. Combine flour, baking powder, nutmeg, cinnamon, baking soda and salt in a medium bowl. Beat the butter and sugar in a large bowl with a mixer on medium-high speed until light and fluffy, approximately three minutes. Beat in the eggs, egg yolk and vanilla and mix until combined.
Add 1/2 of the flour mixture to the butter mixture and mix until well incorporated. Add in half the sour cream and mix until incorporated. Repeat with remaining dry mixture and sour cream. Pour batter into pan that has been prepared and set aside.
Combine flour, brown sugar, cinnamon, nutmeg and salt in a bowl and mix well. Work in the butter with a pastry blender until crumbs have formed. Sprinkle the topping over the cake batter. Bake until golden brown and a toothpick inserted into the center comes out clean, 1 hour to 1 hour 10 minutes for a 9" pan, or 50 minutes to 1 hour for a 10" pan. Remove and place on a rack and let cool 20 minutes, then remove the springform ring and let cool completely.
Stir together the confectioners' sugar, salt, nutmeg and 3 tablespoons eggnog in a medium bowl until smooth. If the glaze is too thick, gradually whisk in the remaining 1 tablespoon eggnog as needed. If glaze is to thin, add more powdered sugar, one tablespoon at a time. Spoon or pipe glaze over cake prior to serving. Entire cake can be covered with glaze or each piece can be glazed independently.