Preheat oven to 350 degrees F. Coat a 9-by-13-inch baking pan with cooking spray

Process graham crackers, oats, 2 tablespoons sugar, 1/4 cup flour and butter in a food processor until finely ground. Add milk; pulse until completely moistened.

Transfer the graham cracker mixture to the prepared pan and evenly pat into the bottom. Bake for 10 minutes. Cool on a wire rack for 20 minutes.

Meanwhile, reduce oven temperature to 325 degrees . Beat both cream cheeses and the remaining 1/2 cup sugar in a large bowl with an electric mixer at medium speed until creamy, scraping down the sides occasionally. Beat in squash puree until smooth. Beat in eggs one at a time. Finally, beat in vanilla, cinnamon, salt and the remaining 3 tablespoons flour. Scrape the filling into the pan, spreading evenly over the crust.

Bake until set and the edges are light brown, about 35 minutes. Let cool completely on a wire rack, then refrigerate for at least 1 hour before cutting into bars.

To make your own squash puree, halve and seed one medium acorn or butternut squash. Place, cut-side down, on a lightly greased baking sheet. Bake in a preheated 375 degrees F oven until soft, about 50 minutes. Cool, then scrape out the flesh with a fork. Or simply use frozen (thawed) or canned squash puree. Find frozen squash puree near other vegetables in the freezer section and canned squash near the canned pumpkin.

MAKE AHEAD TIP: Cover and refrigerate for up to 2 days.