Step 1: Preheat your oven to 350°F (175°C) for even baking.
Step 2: Grease and flour a standard loaf pan (9x5 inches) to prevent sticking.
Step 3: Cream together the softened butter and sugar until light and fluffy, about 3-5 minutes.
Step 4: Add the eggs one at a time, mixing well after each addition.
Step 5: Mix in baking powder, vanilla extract, and salt until well combined.
Step 6: Incorporate the sour cream until fully integrated.
Step 7: Whisk together flour and cornstarch in a separate bowl, then add to wet ingredients gradually, mixing on low speed.
Step 8: Pour the batter into the prepared loaf pan, smoothing the top.
Step 9: Bake for about 60-70 minutes, or until a toothpick comes out clean.
Step 10: Let the cake cool in the pan for 10 minutes, then transfer to a cooling rack to cool completely.