Step 1: Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan, or line it with parchment paper for easy removal.
Step 2: In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Set aside.
Step 3: In a large mixing bowl, cream together the softened unsalted butter and granulated sugar with an electric mixer until light and fluffy (about 2-3 minutes).
Step 4: Add the vegetable oil and beat until well combined.
Step 5: Beat in the eggs one at a time, mixing well after each addition. Scrape down the sides of the bowl as needed.
Step 6: Stir in the vanilla extract, lemon extract (if using), lemon zest, and fresh lemon juice until just combined.
Step 7: Gently fold in the sour cream until fully incorporated.
Step 8: Gradually add the dry ingredients to the wet ingredients in three additions, mixing on low speed until just combined. Be careful not to overmix.
Step 9: Pour the batter evenly into the prepared loaf pan. Bake for 50-60 minutes, or until a wooden skewer inserted into the center comes out clean. If the top browns too quickly, tent loosely with aluminum foil.
Step 10: Let the loaf cool in the pan for 15 minutes before carefully transferring it to a wire rack to cool completely.
Step 11: While the loaf cools, prepare the glaze: In a small bowl, whisk together the powdered sugar and fresh lemon juice until smooth. Adjust consistency by adding more powdered sugar for a thicker glaze or more lemon juice for a thinner glaze.
Step 12: Once the loaf is completely cool, drizzle the lemon glaze evenly over the top, allowing it to drip down the sides. Let the glaze set for a few minutes before slicing and serving.