To start, make the caramel sauce by melting 2 tablespoons of butter and 2 tablespoons of brown sugar in a medium sauce pan over medium low heat.
When melted, stir in the sweetened condensed milk and continue cooking, stirring constantly, until the mixture thickens and darkens to a caramel color, about 20 minutes.
Remove from the heat and stir in the peanut butter and vanilla.
To make the crust, combine the flour, oatmeal, and remaining 1/2 cup of brown sugar in a large bowl. Melt the remaining 1 1/2 cups of butter and stir into the oatmeal mixture.
Press half of the oatmeal mixture into the bottom of a 9x13 baking dish and bake in a preheated 350 degree oven for 10 minutes. Remove from the oven.
Sprinkle the chocolate chips over the oatmeal crust. Spread the caramel peanut butter mixture over the chocolate chips and crumble the remaining oatmeal crust mixture over the top.
Return to the oven and continue baking for 15 minutes.
Remove from the oven and cool completely before cutting.