Preheat the oven to 350°F. Line an 8 by 8-inch baking pan with foil or parchment, leaving an overhang.

In the bowl of a food processor, pulse the graham crackers until finely ground. You should have about 1 cup crumbs.

Add the melted butter and pulse until moistened. Press the mixture firmly into the bottom of the prepared pan. Bake for about 10 minutes, or until lightly golden brown and fragrant. Let cool.

In the bowl of an electric mixer, beat the cream cheese and sugar on medium-high speed until well combined and smooth, scraping down the edges as necessary. Beat in the lemon zest, lemon juice, eggs, and vanilla until combined. Add in the flour and salt and beat until just combined. Spread the mixture over the crust.

In a food processor or blender, puree the raspberries until smooth. Press through a fine mesh strainer, discarding any seeds and pulp that remain. Stir in the sugar. Dollop the unbaked cheesecake batter with spoonfuls of the raspberry puree. Use a knife or skewer to make swirls.

Bake for 30 minutes, or until set at the edges but ever so slightly jiggly in the middle. Don't overbake. Cool completely in the pan on a wire rack. Cover and chill the cheesecake in the fridge until very cold, at least 3 hours. The cheesecake can be stored in the fridge for up to 2 days.

Before serving, use the foil or parchment to remove the cheesecake from the pan and onto a work surface. Cut into 15 squares. Serve chilled.