Make the crust. Stir the graham cracker crumbs, sugar, and salt in a bowl. Pour in the melted butter and mix until the crumbs look like damp sand. If you squeeze a handful, it should clump. If it falls apart, add another teaspoon of melted butter.
Press and bake the crust. Tip the crumbs into your prepared pan and press firmly into an even layer. I use the flat bottom of a measuring cup to get the edges neat. Bake for 10 minutes, then set aside to cool slightly while you make the filling.
Beat the cream cheese. In a mixing bowl, beat the cream cheese with an electric mixer on medium speed until perfectly smooth, about 1 to 2 minutes. Scrape the bowl. Don’t rush this part; smooth cream cheese equals smooth bars.
Add sugar, then eggs. Beat in the granulated sugar until combined. Add the eggs one at a time, mixing on low just until each is incorporated. Scrape the bowl again.
Finish the filling. Mix in the sour cream, vanilla, and salt on low until silky. Fold in 3/4 cup of the chopped Butterfingers. Keep the rest for the top.
Assemble. Pour the filling over the warm crust and smooth the top. Sprinkle the remaining Butterfinger pieces evenly. Some will sink a little. That’s fine.
Bake. Bake at 325°F for 30 to 36 minutes, until the edges look set and the center wobbles slightly when you nudge the pan. You’re looking for a gentle jiggle, not sloshy.
Cool gradually. Turn off the oven, crack the door, and let the bars sit inside for 10 minutes. Then remove to a rack to cool to room temperature, about 1 hour. This small pause helps prevent cracks.
Chill. Cover and refrigerate for at least 3 hours, preferably overnight. The texture settles and the flavors mellow. It’s worth the wait.
Finish and slice. If you like, drizzle with melted chocolate and add a tiny pinch of flaky salt. Lift the slab out using the parchment and cut into 12 bars with a sharp knife wiped clean between cuts. Small squares are rich and satisfying.