First off, We know that “streuseled” isn’t a real word. But we also feel strongly that it should be. “Culinarium” isn’t real either but that obviously didn’t stop us. — Chef Amy
1-1/4 Cups coarsely chopped walnuts
1-1/4 Cups (packed) golden brown sugar
4-1/2 tsp Ground Cinnamon
4-1/2 tsp unsweetened cocoa powder
6 Tbsp dried currants
3 Cups cake flour
1-1/2 tsp baking soda
1-1/2 tsp baking powder
3/4 tsp Salt
3/4 Cup (1 1/2 sticks) unsalted butter, room temperature
1-1/2 Cups sugar
3 large eggs
1 Tbsp Vanilla Extract or Vanilla Paste
1 16-oz container sour cream
1 Cup powdered sugar
1 Tbsp milk
Preheat oven to 350°F. Butter a 12-cup Bundt pan. Mix first 5 ingredients (walnuts, brown sugar, cinnamon, cocoa, and currants) in a small bowl. Set this nut mixture aside. Sift flour, baking soda, baking powder and salt into another medium bowl.
Using electric mixer, cream the butter with 1-1/2 cups sugar in a large mixing bowl until blended. Beat in eggs, 1 at a time. Add the vanilla. Mix dry ingredients and sour cream alternately into butter mixture, in 3 additions. Beat batter on high 1 minute.
Pour 1/3 of batter into prepared Bundt pan. Sprinkle with half of nut mixture. Spoon 1/3 of batter over the top of the layer of nut streusel. Sprinkle with remaining nut mixture. Spoon remaining batter over the top.
Bake cake until tester inserted near center comes out clean, about 1 hour. Remove bundt pan from the oven, and cool cake in the pan on rack 10 minutes. Carefully cut around pan sides to loosen cake. Turn cake out onto cooling rack and let cool 1 hour. Transfer to cake plate or serving platter.
Whisk powdered sugar and milk in small bowl until smooth. Drizzle over coffee cake. Serve slightly warm, or at room temperature.
MAKE AHEAD: Can be prepared up to 1 day ahead. Cool completely. Wrap in foil and let stand at room temperature.