Make sure to scrape the paddle and the sides of the bowl regularly when making the filling in order to achieve a silky, smooth texture.
1. Adjust oven rack to middle position and heat oven to 325 degrees. Make foil sling for 8-inch square baking pan by folding 2 long sheets of aluminum foil so each is 8 inches wide. Lay sheets of foil in pan perpendicular to each other, with extra foil hanging over edges of pan. Push foil into corners and up sides of pan, smoothing foil flush to pan. Grease foil.
2. FOR THE CRUST: Process graham crackers in food processor to fine, even crumbs, about 30 seconds. Add melted butter, sugar, flour, and salt and pulse to combine, about 10 pulses. Sprinkle mixture into prepared pan and press firmly into even layer. Bake until crust is fragrant and beginning to brown, 12 to 15 minutes, rotating pan halfway through baking. Let crust cool completely in pan on wire rack.
3. FOR THE FILLING: Using stand mixer fitted with paddle, beat cream cheese on medium speed until smooth, 1 to 3 minutes, scraping down bowl as needed. Gradually add sugar and beat until incorporated, about 1 minute. Add eggs, one at a time, and beat until combined, about 30 seconds. Add sour cream, lemon juice, and vanilla and mix until incorporated, about 30 seconds.
4. Pour filling over crust and spread into even layer. Bake until edges are set but center still jiggles slightly, 35 to 40 minutes, rotating pan halfway through baking. Let cheesecake cool completely in pan on wire rack, about 2 hours. Refrigerate until thoroughly chilled, at least 3 hours or up to 24 hours. Using foil overhang, remove cheesecake from pan. Cut into 16 pieces before serving. (Uncut bars can be frozen for up to 1 month; let wrapped bars thaw at room temperature for 4 hours before serving.)