Combine flour, baking soda, salt, sugar, crackers and melted butter in that order. Spread half of the mixture in a lightly buttered 23 cm pie plate, Cover with blueberry pie filling which has been mixed with lemon juice, and then top with the remaing soda cracker mix.Bake in preheated 190ºC F oven for 25-30 minutes. Cool on rack. Serve with lightly sweetened-vanilla flavored whipped cream or with vanilla ice cream. This pie makes its own crust.