Prep the pan and oven. Heat the oven to 325°F (163°C). Line a 9x13-inch pan with parchment, leaving overhang on the long sides so you can lift the bars out later.
Make the crust. Stir together graham cracker crumbs, sugar, melted butter, and salt until the mixture resembles wet sand.
Press firmly into the prepared pan, packing it tight and even. Use the bottom of a measuring cup for a smooth surface.
Par-bake the crust. Bake for 8–10 minutes, until lightly fragrant. Set aside to cool slightly while you make the filling.
Beat the cream cheese. In a large bowl, beat the softened cream cheese on medium speed until smooth and creamy, 1–2 minutes.
Scrape the bowl to avoid lumps.
Add sugar and flavorings. Beat in the sugar until combined, then add sour cream, vanilla, lemon juice, lemon zest (if using), and salt. Mix until silky and uniform.
Mix in eggs. Add eggs one at a time on low speed, mixing just until incorporated. Do not overmix; too much air can cause cracks.
Fill and bake. Pour the batter over the warm crust and smooth the top. Bake at 325°F (163°C) for 25–30 minutes, or until the edges are set and the center still has a slight wobble.
The top should look matte, not wet.
Cool gradually. Turn off the oven, crack the door, and let the pan sit for 10 minutes. Then remove to a cooling rack and cool to room temperature.
Chill. Cover and refrigerate for at least 4 hours, preferably overnight. Chilling sets the texture and makes clean slices.
Add the cherry topping. If using canned filling, gently spoon it over the chilled cheesecake in an even layer.
For homemade: simmer cherries, sugar, and lemon juice for 4–6 minutes until juicy. Stir in the cornstarch slurry and cook 1–2 minutes more until glossy and thick. Cool completely before spreading on top.
Garnish and serve. Drizzle with melted white chocolate or add sprinkles for a Valentine’s touch.
Lift the bars out using the parchment and cut into squares or rectangles with a sharp knife. Wipe the blade between cuts for tidy edges.