Cinnamon Swirl Buttermilk Pound Cake

The second recipe I tried within a week from Tish Boyle's The Cake Book, this one was made for an office birthday and got excellent reviews there. It is not a terribly sweet cake, but sturdy and scrumptious, and would make an excellent brunch item.

Cinnamon Streusel
1/2 c all-purpose flour
1/3 c packed light brown sugar
1/4 tsp cinnamon
pinch of salt
3 Tbsp unsalted butter, melted

Buttermilk Pound Cake
2 c all-purpose flour
1/2 c cake flour
1 tsp baking powder
1/4 tsp baking soda
1/2 tsp salt
1/8 tsp ground cardamom
1 c unsalted butter, softened
2 c granulated sugar
3 large eggs
2 tsp vanilla extract
1 tsp finely grated orange zest
1 c buttermilk

1. Position a rack in the center of the oven. Preheat oven to 325F. Grease and flour a 10-inch Bundt pan.
2. To make the streusel, in a small bowl, whisk together the flour, brown sugar, cinnamon, and salt, breaking up any large lumps of brown sugar. Add the melted butter and stir until blended and crumbly.
3. To make the pound cake, sift together the flours, baking powder, baking soda, salt, and cardamom in a medium bowl. Whisk to combine, and set aside.
4. In an electric mixer, beat the butter until very creamy, about two minutes. Gradually add the sugar and beat at medium-high speed until well blended and light, about four minutes. Add the eggs one at a time, beating well after each addition and scraping down the sides of the bowl. Beat in the vanilla extract and orange zest. At low speed, add the dry ingredients in three additions, alternating with the buttermilk in two additions. Mix until just combined.
5. Scrape half the batter into the pan and smooth into an even layer. Sprinkle the streusel evenly over the batter. Scrape the remaining batter on top and smooth.
6. Bake 65-75 minutes or until a cake tester comes out clean. Cool the cake in the pan on a rack for 15 minutes. 
7. Invert the cake onto the rack and cool completely. 
8. Dust with confectioners' sugar before serving.