Press half of crumb mixture into 9x13 inch pan. Reserve remaining crumb mixture for topping.
Bake for 15 minutes in 350 degree oven.
While this bakes, make the caramel. Melt 1 stick butter in a heavy saucepan. Add 3/4 cup brown sugar and can of sweetened condensed milk. Bring to boil, then reduce to simmer stirring regularly. Simmer 7-10 minutes, then remove from heat. Add 1/4 cup flour to the caramel and whisk until smooth.
1 can sweetened condensed milk, 3/4 cup brown sugar, 1/4 cup flour, 1/2 cup unsalted butter
Remove crust from oven. Immediately sprinkle with chocolate chips and pecans. Drizzle caramel sauce over chips and nuts. Sprinkle remaining crumb mixture evenly on top.
12 ounces semi-sweet chocolate chips, 1 cup chopped pecans
Return pan to oven and bake 18-20 minutes more, until crumbs are light golden brown. Remove pan from oven and cool for 2 hours. Cut into small squares.