Heat oven to 375°F.
Mix flour, margarine, and powdered sugar until crumbly; sprinkle in water 1 teaspoon at a time, stirring until dough forms.
Press about 3 tablespoons of dough in bottom and up sides of each of 4 ungreased 6 ounce custard cups to within 1/2 inch of the top.
Bake until golden brown, 10 to 12 minutes; let cool 10 minutes. Carefully remove from cups with a small metal spatula; let cool completely on wire rack.
Fill each cup with 1/3 cup yogurt; garnish with fresh fruit if you like.