Preheat the oven to 350°F. Line an 8×8-inch baking pan with parchment, leaving an overhang for easy lifting.

In a medium bowl, whisk together 1 3/4 cups flour, 1/2 cup sugar, and 1/2 teaspoon salt. Cut in 3/4 cup cold cubed butter with a pastry blender or two knives until mixture resembles coarse crumbs with pea-sized pieces.

Press about two-thirds of the mixture evenly into the bottom of the prepared pan to form the crust. Reserve the remaining dough in the fridge for the topping.

Bake the pressed crust at 350°F for 12–14 minutes until the edges are just set and beginning to color. Remove from oven and set aside while you make the filling.

Slice and dice the peaches, then toss with 2 tablespoons sugar and 1 teaspoon lemon juice. Let sit 10–15 minutes to macerate, then drain off any excess liquid and pat peaches dry with paper towels.

In a medium bowl, beat the softened cream cheese with 1/3 cup sugar, 1 large egg, 2 teaspoons cornstarch, 1 teaspoon vanilla, and a pinch of salt until smooth and slightly fluffy. Fold the drained peaches into the cream mixture gently.

Spread the peach and cream mixture over the warm partially baked crust in an even layer. Crumble the reserved dough over the filling; press gently in places if needed so the topping adheres.

Bake at 350°F for 30–35 minutes until the top is golden and the center is set but with a slight jiggle. If using sliced almonds or oats, sprinkle them on for the last 8–10 minutes of baking so they toast without burning.

Cool the pan on a wire rack for at least 1 hour, then refrigerate for 30 minutes to firm the filling. Use the parchment overhang to lift the slab from the pan and slice into 12 bars with a sharp knife warmed under hot water and dried between cuts.