Preheat the oven to 325 F. Line an 8 x 8 inch square pan with aluminum foil, leaving a 1-inch overhang.
In a food processor, process the graham crackers until you have fine crumbs, about 20-30 seconds. Add the melted butter and pulse until well combined.
Press the crust into the bottom of the prepared pan, firmly and evenly. Using the bottom of a glass helps.
Bake the crust in the preheated oven for 12 minutes.
Filling
In the bowl of a stand mixer, beat the softened cream cheese on medium speed until completely smooth.
Add the sugar and beat on medium speed until incorporated, about 2 minutes.
Add the eggs, sour cream, lemon zest, lemon juice, and vanilla extract, and beat until perfectly smooth, scraping down the sides of the bowl as needed, about 2 minutes more.
Pour the filling into the pan. Bake in the preheated oven for 35-40 minutes, until the sides are set but the center is still slightly jiggly.
Cool the bars completely, about 2 hours, and transfer to the fridge to chill, another 3-4 hours.
Lift the bars out of the pan using the foil overhang. Slice the bars into 9 or more squares with a long, sharp knife, wiping the blade between each cut.
Garnish the bars with fruit, whipped cream, or lemon slices, if desired.
Notes
Bars can be frozen, cut or not, for 2-3 months. Thaw completely at room temperature, 3-4 hours, before serving.