Cream butter; add sugar and beat well.
Beat in eggs one at a time.
Add vanilla.
Gradually stir in sifted dry ingredients.
Spread 3/4 of dough in a lightly greased 8x11 or 8x8 inch baking pan.
Spread blueberry pie filling over dough.
Spoon remaining dough over pie filling, spreading lightly. *Not all pie filling will be covered.
In a separate small bowl, combine streusel ingredients and sprinkle over the top of bars.
Bake at 375 degrees for 35-40 minutes.
Cool 15 minutes.
In a small bowl, mix powdered sugar, milk, and vanilla until smooth; drizzle over bars.