Step 1

Place 2 1/2 pounds cream cheese in the bowl of a stand mixer (or large bowl if using an electric hand mixer). Place 1/3 cup sour cream, 4 large eggs, and 1/4 cup heavy cream on the counter. Let sit at room temperature until the cream cheese is softened, about 1 hour.

Step 2

Arrange a rack in the lower third of the oven and remove any racks above it. Heat the oven to 350°F. Coat a 9-inch springform pan with cooking spray. Wrap the bottom and outside of the pan with 3 layers of heavy-duty aluminum foil to prevent any water from entering the pan.

Step 3

Place 6 tablespoons unsalted butter in a medium microwave-safe bowl and microwave until melted, 30 to 45 seconds. (Alternatively, melt on the stovetop and pour into a medium bowl.) Break up 15 whole graham cracker sheets with your hands into large pieces and place in a food processor fitted with the blade attachment. Add 1/2 teaspoon kosher salt and pulse until fine crumbs form, about 12 (1-second) pulses. Transfer to the bowl with melted butter and stir until combined and it looks like wet sand.

Step 4

Transfer to the springform pan and use the bottom of a measuring cup or glass to press the crust into an even layer on the bottom.

Step 5

Bake until golden brown and fragrant, about 15 minutes. Transfer the pan to a wire rack and let cool while you make the filling.

Step 6

Bring a kettle or large saucepan of water to a boil for the water bath. Meanwhile, make the filling.

Step 7

Finely grate the zest of 4 to 6 key limes until you have 1 tablespoon. Juice the limes until you have 1/4 cup.

Step 8

Beat the cream cheese with the paddle attachment on medium-low speed, stopping to scrape the bowl well with a rubber spatula as needed, until smooth, creamy, and no lumps remain, 1 1/2 to 2 1/2 minutes. Do not overmix.

Step 9

Add the lime zest, 1 1/2 cups granulated sugar, and 1/2 teaspoon kosher salt. Beat on medium-low speed, scraping the bowl as needed, until slightly fluffy, smooth, and has a texture similar to a thick frosting, 1 1/2 to 2 1/2 minutes.

Step 10

Add the lime juice and sour cream beat on medium-low speed until just combined, about 15 seconds. With the mixer still on medium-low speed, beat in the eggs one at a time, waiting until each egg is just incorporated before adding the next. Stop and scrape down the bowl as needed.

Step 11

Add the heavy cream and beat on medium-low speed until just combined, 6 to 10 seconds more. Do not overmix. Scrape down the paddle attachment and sides of the bowl with a flexible spatula. Give the batter a couple good stirs by hand, making sure to scrape the bottom of the bowl, to ensure everything has been incorporated.

Step 12

Pour into the cooled crust and smooth the top. Pop any bubbles on the surface with the tip of a paring knife, toothpick, or spatula.

Step 13

Place the springform pan in a roasting pan or high-sided baking dish large enough to hold. Place on the oven rack. Taking care to not splash any water onto the cheesecake, carefully pour in enough water into the roasting pan or baking dish to go halfway up the side of the springform pan.

Step 14

Bake until slightly puffed and the edges are set, but the center still jiggles when you gently shake the pan, about 1 hour 10 minutes to 1 hour 15 minutes. It should not look wet, and a golden color on top is okay.

Step 15

Turn the oven off but leave the cheesecake in the oven. Prop the door open a crack with a wooden spoon. Let the cheesecake cool slowly in the turned-off oven for 1 hour.

Step 16

Carefully remove the roasting pan or baking dish from the oven. Remove the cheesecake from the water bath, and remove the foil. Place the cheesecake on a wire rack and let cool completely, 1 1/2 to 2 hours. The bottom of the springform pan should be at room temperature.

Step 17

Refrigerate uncovered for at least 4 hours and up to overnight to completely set. To serve, run a paring knife or small offset spatula around the cheesecake. Remove the outer ring from the springform pan. Serve the cheesecake from the bottom of the springform pan, or use a large offset spatula to carefully transfer it to a serving platter or cake stand. Top with whipped cream and key lime zest and slices if desired.