Step 1: Make the Red Velvet Cake Layer

1. Preheat the oven: Preheat your oven to 350°F (175°C). Grease and line a 9-inch springform pan with parchment paper.
2. Mix the dry ingredients: In a medium bowl, sift together the flour, cocoa powder, baking soda, and salt. Set aside.
3. Combine the wet ingredients: In a small bowl, mix buttermilk, vinegar, vanilla extract, and red food coloring until well combined.
4. Cream the butter and sugar: In a large bowl, use an electric mixer to cream the butter and sugar until light and fluffy, about 2–3 minutes. Add the egg and beat until fully incorporated.
5. Combine wet and dry ingredients: Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk mixture, starting and ending with the dry ingredients. Mix just until combined.
6. Bake the cake layer: Pour the batter into the prepared springform pan and bake for 18–20 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool completely in the pan.

Step 2: Make the Cheesecake Layer

1. Prepare the cheesecake batter: In a large bowl, beat the cream cheese and sugar together until smooth and creamy, about 2–3 minutes. Add the eggs one at a time, mixing well after each addition. Beat in the sour cream and vanilla extract until fully incorporated.
2. Layer the cheesecake: Pour the cheesecake batter over the cooled red velvet cake layer in the springform pan. Smooth the top with a spatula.
3. Bake the cheesecake: Place the springform pan in a large roasting pan and add enough hot water to the roasting pan to come halfway up the sides of the springform pan (this creates a water bath to prevent cracks). Bake at 325°F (160°C) for 50–55 minutes, or until the cheesecake is set around the edges but still slightly jiggly in the center.
4. Cool the cheesecake: Turn off the oven and crack the door open slightly. Let the cheesecake cool in the oven for 1 hour to prevent cracking. Then, transfer it to a wire rack to cool completely. Chill in the refrigerator for at least 4 hours or overnight.

Step 3: Make the Strawberry Topping

1. Cook the strawberries: In a medium saucepan, combine the sliced strawberries, sugar, and lemon juice. Cook over medium heat, stirring occasionally, until the strawberries release their juices and soften, about 5–7 minutes.
2. Thicken the topping: In a small bowl, mix cornstarch with water until smooth. Stir this mixture into the strawberry sauce and cook for an additional 2–3 minutes, or until thickened. Remove from heat and let cool completely before using.

Step 4: Assemble the Cheesecake

1. Add the strawberry topping: Once the cheesecake is fully chilled, spread the cooled strawberry topping evenly over the top.
2. Garnish and serve: Decorate the cheesecake with whipped cream, fresh strawberries, or white chocolate shavings if desired. Slice and serve chilled.