1Prepare the pie crusts per package instructions, or make up your own favorite dough.
In a large bowl, combine the brown sugar, flour, and salt. Be sure to break up any clumps of brown sugar. In a smaller bowl, mix together the melted margarine, beaten eggs, vanilla, and milk; beat well. Add this wet mixture to the brown sugar mixture and blend very well with a handheld mixer. Pour into the pie crust(s) and bake at 350F for about 30 minutes for a regular crust, 60-70 minutes for a deep-dish crust, or until set (just a wee bit wobbly) in the middle. Let cool completely before slicing and serving.