Preheat the oven to 350°F (175°C). Grease and flour a loaf or bundt pan. Zest and juice the lemons. Rinse and dry the blueberries.

In a large bowl, cream the softened butter and sugar until light and fluffy, about 3–4 minutes. Beat in the eggs one at a time, scraping the bowl. Add vanilla extract and mix.

In another bowl, whisk together the flour, baking powder, and salt until evenly mixed.

Add the dry ingredients and the sour cream to the wet mixture in three parts, alternating starting and ending with the flour. Stir in lemon zest and juice.

Toss the blueberries with 1 teaspoon of flour; gently fold them into the batter to prevent sinking. Optionally stir in poppy seeds or almond extract.

Pour the batter into the prepared pan and smooth the top with a spatula. Tap the pan gently to release any air bubbles.

Bake for 55–65 minutes, or until the top is golden and a toothpick in the center comes out clean or with moist crumbs.

Let the cake cool completely in the pan before turning onto a wire rack. Drizzle with lemon glaze or spread with cream cheese frosting as desired.