Orange-sour cream-poppy seed loaf cake

I made this cake to take as a dessert for a dinner we went to recently. I really didn't feel like going out to the store, so I was looking all through my cookbooks to find a dessert that I could make with ingredients I had on hand. I found this sour cream-poppy seed cake in my Tassajara Cookbook and thought it would be perfect. I like poppy seed cakes/muffins to have some citrus in them, so I decided to add some orange, a blood orange actually. You can use any type of orange (or lemon) you would like. This cake was really moist, light, and flavorful and everyone gobbled it up! 

Orange-sour cream-poppy seed loaf cake
1/2 cup unsalted butter, room temperature
3/4 cup sugar
3 eggs, separated
1 teaspoon pure vanilla extract
1/2 cup unbleached all-purpose flour
1/2 cup white whole wheat flour
1/2 teaspoon sea salt
1/2 teaspoon baking soda
1/2 cup sour cream
1/4 cup poppy seeds
zest of one orange
juice of one orange, optional
2-4 tablespoons icing sugar, optional

Preheat the oven to 350 degrees. Butter and flour a 9-inch loaf pan (or spray with a non-stick cooking spray).

Using a stand or hand mixer, cream the butter and sugar until light and fluffy. Beat in the egg yolks one at a time and add the vanilla.

In a medium bowl, whisk together the flour, salt, and baking soda. Fold them into the butter mixture alternating with the sour cream.

In a large bowl, beat the egg whites until they form stiff peaks. Gently fold them into the batter. Then fold in the poppy seeds and orange zest until everything is just combined. Pour the batter into the loaf pan.

Bake for approximately 45 minutes, until the top is lightly golden and an inserted toothpick comes out cleanly. Let cool in the pan on a wire rack. Serve warm or room temperature.

To add a glaze, add the orange juice in a small bowl and add icing sugar a tablespoon at a time, stirring until the consistency is slightly thickened. Drizzle the desired amount of glaze over the top of the cake with a fork. Let dry/harden completely before covering, or serve immediately.

This cake has  been submitted to: Sweets for a Saturday at Sweet as Sugar Cookies

What was I cooking one year ago?: apple almond bread