Preheat your oven to 350°F (175°C). Grease a standard loaf pan thoroughly with butter or non-stick spray, and line the bottom with parchment paper for easy removal.
In a medium mixing bowl, whisk together the flour, baking powder, baking soda, and salt. This ensures the leavening agents are evenly distributed for a consistent rise.
In a large bowl or stand mixer, beat the butter and sugar on medium-high speed for about 3 to 4 minutes, until the mixture becomes pale, fluffy, and aerated. Creaming the butter and sugar well at this stage is key to creating a tender crumb.
Add the eggs one at a time, mixing well after each addition until fully incorporated. The batter may look slightly curdled after adding the eggs, but it will smooth out once the remaining ingredients are added.
Stir in the sour cream, followed by the oil, lemon zest, lemon juice, and vanilla extract. Mix until the batter is smooth and creamy. The combination of sour cream and oil helps create a moist texture with a subtle tang.
Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed just until combined. Be careful not to overmix, as this can toughen the cake.
Gently fold in the poppy seeds with a spatula, distributing them evenly throughout the batter without deflating it.
Pour the batter into the prepared loaf pan, spreading it evenly. Tap the pan lightly on the counter to release any large air bubbles.
Bake in the center of the oven for approximately 60 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs. The top should be golden and domed, with slight cracks indicating doneness.
