Preheat the oven to 325°F. Place a large roasting pan on the lower third rack of the oven. Bring a kettle of water to a boil on the stove.
Prepare a 9-inch springform pan: spray the inside with nonstick spray and line the bottom with a round of parchment paper. Wrap a double layer of heavy-duty foil around the bottom and up the sides of the pan, sealing seams so water from the water bath cannot seep in.
Make the cheesecake batter: in a large bowl, use an electric mixer to beat the Two 8-ounce packages cream cheese (room temperature) until smooth and creamy, about 1–2 minutes. Add 2/3 cup granulated sugar and a pinch of salt; blend for 2 minutes, scraping down the bowl as needed.
Add the cheesecake eggs one at a time, mixing briefly after each until incorporated. Mix in 1/3 cup sour cream, 1/3 cup heavy whipping cream, and 1 teaspoon vanilla extract; mix until the batter is smooth.
Pour the cheesecake batter into the prepared springform pan. Place the springform pan into the roasting pan on the oven rack. Carefully pour the boiling kettle water into the roasting pan until the water comes about 1 inch up the foil around the cheesecake pan.
Bake the cheesecake at 325°F for 45 minutes, until the top is set to the touch and not jiggly.
Remove the roasting pan from the oven. Carefully lift the springform pan out of the water bath and place it on a wire rack. Let the cheesecake cool on the rack for at least 1 hour.
After cooling, place the cheesecake (still in the springform pan and foil) into the freezer and freeze completely, 4–5 hours or overnight.
When the cheesecake is frozen solid, preheat the oven to 350°F. Prepare two 9-inch round cake pans: spray with nonstick spray and line the bottoms with parchment rounds.
In a medium bowl, sift together 2 1/2 cups all-purpose flour and 1/2 teaspoon salt.
In a large bowl, combine 1 1/2 cups canola or vegetable oil and 1 1/2 cups granulated sugar. Beat with an electric mixer for 2 minutes.
Add the two cake eggs, one at a time, beating briefly after each. Add 1 teaspoon vanilla extract and beat an additional 2 minutes.
In a small bowl, combine 1 teaspoon white vinegar and 1 teaspoon baking soda and stir briefly (the mixture will fizz). Add to this small bowl 1 cup buttermilk and 1 tablespoon green food coloring; stir to combine.
Add the buttermilk/coloring mixture to the cake batter and beat on medium-low speed for 1 minute until blended.
Add the sifted dry ingredients to the batter. Increase the mixer speed to medium-high and beat, scraping down the sides of the bowl, for 2 minutes more.
Divide the batter evenly between the two prepared 9-inch pans. Bake at 350°F for 30–35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs attached.
Let the cakes cool in their pans for 20 minutes. Run a knife around the edges, invert the cakes onto a wire rack, remove the parchment, and cool completely.
Make the frosting: in a large bowl, beat the Two 8-ounce packages cream cheese and 1/2 cup (1 stick) salted butter (both at room temperature) on medium-high speed until creamy and smooth.
Add the One 7-ounce jar marshmallow creme and mix until smooth. Add 1 cup powdered sugar and continue beating, scraping down the sides, until the frosting is smooth and spreadable.
Assemble the cake: place one cooled cake layer on your cake plate or platter. Remove the frozen cheesecake from the freezer, unlock and remove the springform side, then slide a knife under the parchment to release the cheesecake from the pan and peel off the parchment.
Trim the frozen cheesecake as needed so its diameter matches the cake layers. Place the cheesecake layer on top of the bottom cake layer, then place the second cake layer on top of the cheesecake.
Apply a thin crumb coat of frosting to the assembled cake to seal in crumbs. Refrigerate the cake for 30 minutes, or until the crumb coat is set.
Apply the final layer of frosting over the chilled crumb coat. Place a large scoop of frosting on top, use a long spatula or knife to spread it evenly across the top, then spread down the sides until smooth. Decorate as desired.