Preheat oven to 350°F. Spray interiors of jars with cooking spray. Add 2 tablespoons of pecans to each jar.
Whisk together sugar and flour in a large bowl. Add corn syrup, evaporated milk and vanilla using a spoon. Pour a scant 1/4 cup filling into each jar. Place filled jars on a baking sheet.
Bake on center rack of oven for 25 to 35 minutes.
Cool for 2 hours on wire rack before serving.
Serve each with a dollop of whipped cream. Garnish with crumbled cookies if desired.
Note: If using another size jar (other than the 4-ounce size called for), be sure to leave about 3/4-inch between the pecan filling and the rim of the jar to avoid boilovers.