Preheat oven to 325°F (163 °C). Grease and flour a Bundt pan or line a 9×5″ loaf pan with parchment.

In a medium bowl, sift together flour, baking powder, and salt; set aside.

In a large mixing bowl, cream butter and sugar until light and fluffy. Beat in eggs one at a time, then stir in lemon zest, lemon juice, sour cream, buttermilk, and vanilla.

Add half of the flour mixture and mix gently, then the rest of the flour mixture until just combined. Avoid over‑mixing.

Pour batter into prepared pan and smooth the top. Bake for 60–70 minutes (Bundt) or about 55–65 minutes (loaf), until a toothpick inserted into center comes out clean.

Allow cake to cool in pan for 10–15 minutes, then turn out onto a wire rack to cool completely.

Meanwhile, whisk together powdered sugar and lemon juice until smooth. If too thick, add a teaspoon of water or cream.

Drizzle glaze over cooled cake and let it set before slicing.