Step 1

Preheat the oven to 350 degrees. Grease and flour a 10-inch tube pan.

Step 2

Cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment for 4 to 5 minutes, until light. Add the eggs one at a time, then add the vanilla and sour cream. In a separate bowl, sift together the flour, baking powder, baking soda, and salt. With the mixer on low, add the flour mixture to the batter until just combined. Finish stirring with a spatula to be sure the batter is well mixed.

Step 3

For the streusel, place the brown sugar, flour, cinnamon, salt, and butter in a bowl and pinch together with your fingers until it forms a crumble. Mix in the walnuts.

Step 4

Spoon half the batter into the pan and spread it out with a knife. Sprinkle with 3/4 cup streusel. Spoon the rest of the batter in the pan, spread it out, and scatter the remaining streusel on top. Bake for 45 to 55 minutes, until a cake tester comes out clean.

Step 5

Allow to cool on a wire rack for 30 minutes. Carefully transfer the cake, streusel-side up, onto a serving plate. Whisk the confectioners’ sugar and maple syrup together, adding a few drops of water, if necessary, to make the glaze thick but runny. Drizzle the glaze over the cake with a small spoon. Serve at room temperature.

Step 7

Notes: If you don’t have cake flour, you can substitute 2¼ cups all-purpose flour plus ¼ cup cornstarch.

Step 8

If the eggs are cold, place the whole eggs in a bowl of warm water for 5 minutes before cracking them.