Step 1: Preheat the Oven

• Preheat your oven to 350°F (175°C).
• Grease a 9×5-inch loaf pan and line it with parchment paper, allowing the excess to hang over the sides for easy removal.

Step 2: Prepare the Dry Ingredients

• In a medium bowl, sift together the all-purpose flour, baking powder, baking soda, and salt.
• Whisk to ensure everything is evenly combined. Set aside.

Step 3: Cream the Butter and Sugar

• In a large mixing bowl, use an electric mixer to beat the unsalted butter and granulated sugar until light and fluffy, about 3-4 minutes. This step is crucial for achieving a moist and airy texture.
• Scrape down the sides of the bowl as needed to ensure everything is well mixed.

Step 4: Add Eggs and Flavorings

• Add the eggs one at a time, beating well after each addition.
• Mix in the lemon zest, lemon juice, and vanilla extract. The mixture may look slightly curdled; this is normal.

Step 5: Incorporate the Dry Ingredients

• Gradually add the flour mixture to the wet ingredients, alternating with the sour cream.
• Begin and end with the flour mixture, mixing on low speed just until combined. Do not overmix, as this could lead to a dense cake.
• Add the milk and gently fold in the poppy seeds using a spatula.

Step 6: Transfer to the Loaf Pan

• Pour the batter into the prepared loaf pan, spreading it evenly with a spatula.
• Tap the pan gently on the counter to remove any air bubbles.

Step 7: Bake the Cake

• Bake for 60-70 minutes, or until a toothpick inserted into the center comes out clean.
• If the top is browning too quickly, tent it with aluminum foil after 40 minutes of baking.
• Once done, let the cake cool in the pan for 15 minutes before transferring it to a wire rack to cool completely.

Prepare the Vanilla Drizzle

Step 8: Make the Drizzle

• In a small bowl, whisk together the powdered sugar, milk (start with 2 tablespoons and add more as needed), vanilla extract, and a pinch of salt until smooth.
• The drizzle should be thick but pourable. Adjust the consistency by adding more milk or powdered sugar as needed.

Step 9: Drizzle Over the Cake

• Once the cake has completely cooled, use a spoon or a small whisk to drizzle the vanilla glaze over the top.
• Let the glaze set for about 10-15 minutes before slicing.