Prep the pan: Line a 9x9-inch (23x23 cm) square baking pan with parchment, leaving overhang on two sides for easy lifting. Preheat oven to 325°F (163°C).
Make the crust: In a bowl, mix graham crumbs, sugar, and salt. Stir in melted butter until the mixture feels like wet sand.
Press firmly and evenly into the pan. Bake for 10 minutes, then cool while you make the filling.
Soften the cheese: Beat cream cheese on medium speed until completely smooth and fluffy, about 2 minutes. Scrape the bowl well.
Sweeten and stabilize: Add sugar, cornstarch, and salt.
Beat until silky, about 1 minute. Scrape the bowl again.
Add eggs: Beat in eggs one at a time on low speed until just combined. Do not overmix.
Finish the batter: Mix in sour cream and vanilla on low until smooth.
Fold in 3/4 cup chopped mini eggs (and mini chips, if using).
Assemble: Pour batter over the warm crust and smooth the top. Sprinkle the remaining chopped mini eggs evenly over the surface, pressing them in gently.
Bake: Bake at 325°F (163°C) for 28–34 minutes, until the edges are set and the center has a slight jiggle like Jell-O. Avoid browning on top.
Cool gradually: Turn off the oven, crack the door, and let the pan sit for 10 minutes.
Move to a wire rack and cool to room temperature.
Chill: Cover and refrigerate for at least 4 hours, preferably overnight, until fully set.
Slice and serve: Lift out by the parchment. Use a sharp knife, wiping between cuts, to get clean bars. Serve chilled.