In a microwave-safe bowl, melt 1 1/4 cups of butter for about 30 seconds until completely liquid.

In a large bowl, combine melted butter, 1 1/2 cups of quick oats, 2 1/4 cups of all-purpose flour, and 1 1/2 cups of brown sugar.

Press two-thirds of the crust mixture into the bottom of a greased 9x13 inch pan.

In a saucepan, melt 1/4 cup of butter over medium heat, stirring continuously until it bubbles.

Stir in 1 cup of brown sugar until completely smooth.

Gradually add 1/4 cup of milk, stirring, then incorporate 2 teaspoons of vanilla extract and 2 tablespoons of flour.

Bring the mixture to a gentle boil and simmer for about 3 minutes, until it thickens.

Pour the caramel filling evenly over the cooled crust.

Sprinkle the reserved crust mixture over the caramel filling.

Bake at 300°F for 20 minutes, looking for a golden hue on top.

Once cooled, slice into bars and serve at room temperature.