Sour cream streusel coffee cake

This coffee cake is great served warm with a giant cup of coffee in the morning!  I make it when I have houseguests.  The smell of warm cinnamon and brown sugar in the morning is always welcoming.
 
Nut mixture:
1 1/4 cups coarsely chopped walnuts

1 1/4 cups (packed) golden brown sugar

4 1/2 teaspoons ground cinnamon

4 1/2 teaspoons unsweetened cocoa powder

6 tablespoons dried currants

Cake:

3 cups cake flour

1 1/2 teaspoons baking soda

1 1/2 teaspoons baking powder

3/4 teaspoon salt

1.5 sticks unsalted butter, room temperature

1 1/2 cups sugar

3 large eggs

1 tablespoon vanilla extract

1 16-oz container sour cream

Glaze:

1 cup powdered sugar

1 tablespoon milk

  

Preheat oven to 350°F. Grease the Bundt pan. Mix the nut mixture ingredients in small bowl. Set nut mixture aside. Sift flour, baking soda, baking powder and salt into medium bowl. Using electric mixer, beat butter and 1 1/2 cups sugar in large bowl until blended. Beat in eggs 1 at a time. Mix in vanilla. Mix dry ingredients and sour cream alternately into butter mixture in 3 additions. Beat batter on high for 1 minute.

Pour half of batter into prepared pan. Sprinkle with half of nut mixture. Spoon last half of batter over. Sprinkle with remaining nut mixture.

Bake cake until tester inserted near center comes out clean, about 1 hour. Cool cake in pan for 10 minutes. Cut around pan sides to loosen cake. Turn cake out onto a plate and cool for an hour.

Whisk powdered sugar and milk in small bowl until smooth. Drizzle over coffee cake. Serve warm or at room temperature.