Step 1: Preheat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans. Line the bottoms with parchment paper.
Step 2: In a medium bowl, whisk together the flour, sugar, cocoa powder, baking soda, and salt for the red velvet cake. Set aside.
Step 3: In a large bowl, cream the softened butter and egg until light and fluffy. Beat in the vanilla extract.
Step 4: In a separate small bowl, combine the buttermilk, red food coloring, and vinegar.
Step 5: Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk mixture, beginning and ending with the dry ingredients. Mix until just combined. Do not overmix.
Step 6: Divide the batter evenly between the two prepared cake pans. Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean. Let cool in pans for 10 minutes before inverting onto a wire rack to cool completely.
Step 7: Reduce oven temperature to 325°F (160°C). Prepare a 9-inch springform pan by wrapping the outside with heavy-duty foil to prevent water from seeping in during the water bath.
Step 8: In a large bowl, beat the softened cream cheese with granulated sugar and flour until smooth. Add vanilla extract and lemon zest (if using), mixing until just combined.
Step 9: Beat in the eggs one at a time, mixing on low speed until just incorporated after each addition. Do not overmix. Stir in the sour cream until smooth.
Step 10: Place one cooled red velvet cake layer in the bottom of the foil-wrapped springform pan. Carefully pour the cheesecake batter over the cake layer.
Step 11: Place the springform pan in a larger roasting pan. Fill the roasting pan with hot water about halfway up the sides of the springform pan.
Step 12: Bake for 1 hour to 1 hour 15 minutes, or until the edges are set but the center still jiggles slightly. Turn off the oven, prop the door open slightly, and let the cheesecake cool in the water bath in the oven for 1 hour.
Step 13: Remove the cheesecake from the water bath, remove the foil, and let it cool completely on a wire rack. Once cooled, cover and refrigerate for at least 6 hours, or preferably overnight, until thoroughly chilled.
Step 14: Just before serving, prepare the strawberry topping. In a medium bowl, gently toss the sliced strawberries with granulated sugar and lemon juice. Let sit for 10-15 minutes to allow juices to release.
Step 15: Carefully remove the sides of the springform pan from the chilled cheesecake. Place the second red velvet cake layer on top of the cheesecake. Spread the strawberry topping evenly over the top.
Step 16: Slice and serve immediately. Enjoy your decadent Red Velvet Strawberry Cheesecake!