Preheat your oven to 325°F (163°C). Grease an 8x4-inch loaf pan with butter or nonstick cooking spray.

In a large mixing bowl, cream together butter and sugar using an electric mixer for about 3 minutes until light and fluffy. Beat in the eggs, one at a time, scraping down the sides of the bowl as needed. Mix in the lemon zest, lemon juice, and vanilla extract until well combined.

In a separate bowl, whisk together flour, baking soda, salt, and baking powder. Add half of this flour mixture to the wet ingredients, beating until just combined. Mix in the sour cream, followed by the remaining flour mixture, and beat again until smooth.

Pour the batter into the prepared loaf pan and smooth the top. Bake for about 60 minutes, or until a toothpick inserted into the center comes out clean.

Let the cake cool in the pan for 15 minutes, then carefully run a knife around the edges. Turn the loaf out onto a wire rack to cool completely.

In a small bowl, whisk together powdered sugar and lemon juice until smooth. For a thinner consistency, add more lemon juice, one teaspoon at a time.

Set the cooling rack with the loaf over a sheet pan or large cutting board. Drizzle the glaze evenly over the loaf. Let the glaze set completely before slicing and serving.