Grease and flour 2 9x5-inch loaf pans.
Place the butter and shortening in the bowl of a stand mixer fitted with the paddle attachment. Beat on medium speed until creamy.Gradually add the sugars and beat until light and fluffy. Add the eggs, 1 at a time, beating after each addition, just until incorporated. 1 cup unsalted butter, ½ cup vegetable shortening, 2 cups brown sugar, 1 cup granulated sugar, 6 large eggs
In a large bowl, sift the flour, baking powder, and salt together.
3 cups cake flour, 1 teaspoon baking powder, ½ teaspoon kosher salt
In a small measuring cup, mix the milk and vanilla together.
1 cup evaporated milk, 2 teaspoons pure vanilla extract
Add the flour to the butter/sugar mixture alternately with the milk/vanilla mixture. Begin and end with the flour mixture.
Fold in the pecans, if using.
1 cup chopped toasted pecans
Fill the prepared loaf pans with batter and place on the middle rack of a cold oven. Set the temperature to 300°F.NOTE: This Brown Sugar Pound Cake starts in a cold oven. Do NOT preheat the oven. Bake for 70 minutes, test with a toothpick, and check every 5 minutes thereafter. The cake is done when the toothpick inserted in the middle comes out with just a few crumbs attached.
Transfer cooked cake to a cooling rack for 10-15 minutes. Remove from pan and cool completely on the wire rack.