1 cup butter, softened, divided
2/3 cup packed brown sugar
1/2 teaspoon vanilla
1 cup flour
1 cup rolled oats
3/4 cup packed brown sugar
1 1/2 cup whole pecans
2 bars (4 ounces each) sweet baking chocolate
For caramel topping, combine 1/2 cup of the butter and 2/3 cup brown sugar in heavy saucepan. Cook over medium heat stirring constantly until entire surface of mixture is boiling. Boil 1 minute. Remove from heat. Add vanilla. Set aside.
Combine flour, rolled oats, 3/4 cup brown sugar and remaining 1/2 cup butter. Mix until well-blended. Pat firmly into ungreased 13x9x2 inch baking pan. Sprinkle with pecans. Pour caramel topping evenly over pecans and crust. Bake at 350° F until caramel is bubbly, about 15 to 18 minutes. Break chocolate into 1 inch chunks. Sprinkle evenly over caramel layer. Bake 1 minute longer to allow chocolate to melt. Swirl chocolate for a marbled effect. Cool slightly, then chill to set chocolate. Cut into bars.