Cinnamon-Walnut Bundt Cake

1. 1
   Heat the oven to 350°F and arrange a rack in the middle. Generously coat a 12-cup Bundt pan with butter; set aside.
2. 2
   Combine the brown sugar, walnuts, and cinnamon in a small bowl; set aside. Sift the flour, baking powder, baking soda, and salt together into a medium bowl; set aside.
3. 3
   Combine the measured butter and granulated sugar in the bowl of a stand mixer fitted with a paddle attachment. Beat on medium speed until well blended, about 2 minutes. Stop the mixer and scrape down the sides of the bowl and the paddle with a rubber spatula. Return the mixer to medium speed and mix until light in color and aerated, about 4 minutes more.
4. 4
   Turn the mixer to low and add the vanilla. Add the eggs 1 at a time, letting each completely incorporate before adding the next. Stop the mixer and scrape down the sides of the bowl and the paddle with the rubber spatula.
5. 5
   Add the reserved flour mixture, turn the mixer to low, and mix just until smooth. Add the sour cream and mix just until incorporated. Add the reserved brown sugar mixture and mix just until incorporated.
6. 6
   Pour the batter into the prepared pan. Bake until a cake tester or toothpick inserted into the center comes out clean, about 60 to 65 minutes.
7. 7
   Remove to a wire rack and let the cake cool in the pan for 15 minutes. Turn the cake out onto the wire rack and cool completely. Meanwhile, make the glaze. (If you’re not using the glaze, dust the cake with powdered sugar just before serving.)

For the glaze (optional):

1. 1
   Combine all of the ingredients except the vanilla in a medium saucepan over medium heat, whisking until the sugar dissolves, and bring to a simmer. Continue to simmer until slightly syrupy, about 5 minutes. Remove from the heat, stir in the vanilla, and let cool to room temperature, about 20 minutes.
2. 2
   Rewhisk the glaze and drizzle it over the top of the cake (if the glaze seems too thin, add sifted powdered sugar by the tablespoon until it reaches the desired consistency). Let sit until the glaze sets, about 30 minutes. Dust with powdered sugar just before serving.