Preheat oven to 350°. Line a 13″x 9″ baking pan with foil. Grease or spray foil.
Combine flour and 3/4 cup brown sugar. Cut in softened butter until mixture is crumbly. Stir in 1/2 cup chopped pecans. Press mixture into bottom of pan. Bake for 10 minutes.
Using an elecric mixer on medium speed, combine cream cheese and granulated sugar until smooth. Add 1 egg and beat until combined. Stir in chocolate and vanilla extract. Pour over baked crust. Bake 15 minutes. Allow to cool for 10 minutes.
Whisk together 3/4 cup brown sugar, corn syrup, melted butter, and 3 eggs. Stir in 1 & 1/2 cups chopped pecans. Pour over ceam cheese mixture. Bake for 40-45 minutes, or until center is set. Cool completely in pan. Cut into squares and serve.
Makes about 24 bars.