Preheat oven to 325 degrees F. Wrap the outside of a 9-inch springform pan with a double layer of heavy-duty foil. In a bowl, stir together almond flour, melted butter, erythritol, and salt until it resembles wet sand. Press firmly into the bottom of the pan. Bake until just set and barely golden, 10 to 12 minutes. Let cool while you make the filling.

Combine raspberries, erythritol, and water in a small saucepan over medium heat. Cook, mashing with a spoon, until berries break down and mixture thickens slightly, about 5 minutes. Press through a fine-mesh sieve into a bowl to remove seeds. You should have about 3 tablespoons of smooth puree. Let cool completely.

In a large bowl with an electric mixer, beat cream cheese on medium speed until completely smooth and no lumps remain, about 2 minutes. Add erythritol and beat until well combined, scraping down the bowl as needed.

Beat in sour cream until smooth. Add eggs one at a time, beating just until combined after each addition. Mix in vanilla and lemon juice. Do not overbeat once eggs are added or the cheesecake may crack.

Pour filling over the cooled crust. Drop small spoonfuls of raspberry puree randomly over the surface. Use a toothpick or knife tip to swirl the puree into decorative patterns, dragging it through the batter without mixing completely.

Place the foil-wrapped pan in a large roasting pan. Pour hot water into the roasting pan until it reaches halfway up the sides of the springform. Bake until the edges are set but the center still jiggles slightly when nudged, 50 to 55 minutes.

Turn off the oven and crack the door open. Let the cheesecake cool in the oven for 1 hour, then remove from the water bath and cool completely at room temperature. Refrigerate uncovered until fully chilled and firm, at least 4 hours or preferably overnight. Run a thin knife around the edge before releasing the springform.