Preheat the oven to 350ºF. Line a 9×13" baking pan with nonstick foil, leaving about 1″ of overhang. Blend the flour, powdered sugar, cornstarch, and salt in a food processor. Add butter and process until mixture clumps together.
Pour into the baking pan and press evenly. Bake until light golden, 25 minutes. Lower heat to 325ºF.
Meanwhile stir brown sugar, corn syrup, and butter in a medium saucepan over medium-high heat until the sugar dissolves and the mixture boils. Add pecans and cream and boil until it thickens slightly. Stir in vanilla and pour over the baked crust.
Bake until caramel is darker and bubbles thickly, about 20 minutes. Transfer to a rack and cool completely. Use the foil to lift the cookies out and cut into squares.