In a microwavable bowl, mix sugar, flour, and salt.
In a separate bowl, whisk milk and eggs or egg whites. Add to dry ingredients.
Microwave for two minutes and stir.
Return to microwave for one minute intervals, stirring in between, until custard starts to cook. (3 or 4 more minutes. I generally quit cooking after a 1-inch ring of cooked custard forms around the edge of the bowl.).
Remove from microwave and add margarine and vanilla.
Cool slightly and pour into pie crust. Cover with wax paper and refrigerate 2 hours before serving.
*Chocolate Cream Pie: Add 1/2 cup semi-sweet chocolate chips with margarine and vanilla and mix until chips are completely melted. Pour into crust.
*Banana Cream Pie: Slice 2 or 3 bananas into bottom of pie crust before pouring pie filling over top.
*Coconut Cream Pie: Add 1/2 cup coconut with margarine and vanilla and pour into pie crust.
Serve with whipping cream and garnishes of your choice.