Preheat oven 350°. Line a 13 x 9 baking pan with non-stick foil.
In large bowl combine flour, oats, ¾ cup sugar and butter; mix until crumbly.
Set aside 1½ cups crumbs for topping, and press the rest into the prepared pan.
Bake 15 minutes.
Cool completely.
Beat cream cheese until fluffy.
Add condensed milk and vanilla until smooth.
Spread over crust.
In small bowl combine remaining 1 tablespoon brown sugar & cornstarch.
Spoon over cream cheese mixture.
Sprinkle reserved crumb mixture over top.
Bake 40 minutes.
Cool completely on wire rack, then chill before cutting.
Drizzle with dulce de leche.