Prepare the crust: Combine flour, brown sugar, and salt. Cut in cold butter until mixture resembles coarse crumbs. Press into the bottom of a greased 9x13 inch baking pan.
Make the caramel: Combine sugar and corn syrup in a saucepan over medium heat. Cook, without stirring, until golden brown. Carefully stir in heavy cream and butter. Stir in vanilla.
Pour caramel over the crust.
Prepare the crumb topping: Combine flour, brown sugar, and cinnamon. Cut in cold butter until mixture resembles coarse crumbs. Sprinkle over the caramel layer.
Bake at 350°F (175°C) for 30 minutes, or until golden brown.
Let cool completely before cutting into bars.
Notes
Store leftover bars in an airtight container at room temperature for up to 3 days.