Preheat your oven to 350°F (175°C). Grease and flour an 8×4-inch loaf pan.

In a mixing bowl, cream together the softened butter and sugar until light and fluffy, about 3-4 minutes.

Beat in the eggs one at a time, mixing well after each addition.

In another bowl, whisk together the sifted flour, baking powder, and salt. Gradually add this mixture to the butter mixture, alternating with the milk. Stir in the vanilla extract.

Pour the batter into the prepared loaf pan and bake for 45-55 minutes, until a toothpick comes out clean. Allow to cool and slice to fit in a springform pan.

Lower the oven temperature to 325°F (160°C). Combine the graham cracker crumbs, sugar, and melted butter in a bowl. Press firmly into a 9-inch springform pan and bake for 8-10 minutes. Let cool.

Beat softened cream cheese until smooth. Gradually add sugar, eggs, sour cream, and vanilla, mixing until fully combined. Fold in flour or cornstarch and lemon zest.

Layer a third of the cheesecake filling over the crust, place the cooled pound cake, then cover with the remaining filling.

Prepare a water bath by placing the springform pan in a larger baking dish filled with hot water, halfway covering the pan. Bake for 60-75 minutes. Cool in the oven with the door ajar for 1 hour.

Chill in the refrigerator for at least 6 hours or overnight. Prepare topping by mixing sour cream, sugar, and vanilla, spreading over the cheesecake. Bake the topped cheesecake for an additional 8-10 minutes at 325°F.

Garnish and serve, storing leftovers in the refrigerator for up to a week.