Preheat oven to 325°F. Grease and flour a 12-cup tube or bundt pan. If you only have a smaller bundt pan, you can use leftover batter in a smaller pan.
Sift 3 cups of the all-purpose flour and the baking powder together in a mixing bowl.
If using nuts: Stir together nuts with remaining 1/4 cup flour in a separate small mixing bowl. If not using nuts, then add remaining flour to original mixing bowl.
In a large bowl with an electric mixer or hand whisk, cream together the softened butter, dark brown sugar and granulated sugar. Cream for at least 5 minutes, on low to medium-low speed.
Add eggs, one at a time, mixing well after each addition.
Add the sifted flour mixture and the milk, alternating between the two. Continue to mix well and add in vanilla extract.
If including nuts, gently stir those in the batter.
Pour the brown sugar pound cake batter into your pan and bake at 325°F for 1 hour and 15 minutes to 1 hour and 25 minutes. Ovens vary, so be sure to insert a knife or long wooden skewer to test for doneness. Allow the cake to cool before removing from pan.
Notes
This cake makes a lot of batter and if you have extra batter, use it in a smaller pan to make a mini cake, bars, etc.