Preheat the oven to 350 degrees. Spray a 9x5 loaf pan with nonstick baking spray. Set aside.
Add your room temperature butter and sugar to a mixing bowl and mix on high for 5 minutes until light and fluffy.
Mix in the vanilla, sour cream, lemon juice, and eggs.
Add all of the dry ingredients except for the blueberries and mix until just combined.
Fold in the blueberries.
Spread into the prepared loaf pan. Bake for 75-90 minutes, or until a toothpick comes out clean. Allow to cool completely before frosting.
Yuzu Swiss Meringue
Create a double boiler. Heat a pot of water over medium-low and bring to a simmer. Don't fill the water too high. It should never touch the bottom of the glass bowl.
Add the egg whites and sugar to a glass bowl and whisk continually for 4 minutes.
Transfer the bowl to the simmering pot and fit over the top, ensuring the water doesn't touch. Continue to whisk for 4-8 minutes until the mixture is light and frothy. It should read 160 degrees on an instant read thermometer.
Pour the egg mixture into a waiting mixing bowl and beat on high for 10 minutes until it's thick, creamy, and holds its shape. This is called stiff peaks.
Using the same simmering water, melt the yuzu chocolate gently in a glass bowl, using the double boiler method. Stir until completely melted.
Fold the melted chocolate into the Swiss meringue.
Spread on top of the cooled pound cake. You can use a kitchen torch if desired to toast the frosting.