Preheat oven to 350°F (175°C). Grease and line a loaf pan with parchment paper.
In a large bowl, beat butter and sugar until light and fluffy.
Add eggs one at a time, mixing well after each.
In a separate bowl, whisk flour, baking powder, and salt.
Gradually mix dry ingredients into the wet mixture.
Stir in lemon zest, lemon juice, and chopped sage.
Add sour cream (or yogurt) and gently fold until smooth.
Pour into loaf pan and bake 50–60 minutes, or until a toothpick comes out clean.
Let cake cool completely.
Whisk powdered sugar and lemon juice until smooth. Drizzle over cooled cake. Garnish with a sprinkle of sage if desired.