Cut butter into flour until particles are the size of small peas. Sprinkle water over flour mixture; mix with fork.
Gather pastry into a ball; divide into halves. Pat each half into a 12x3-inch long rectangle on an ungreased cookie sheet. Rectangles should be about 3 inches apart.
Topping:
Heat butter and water to a rolling boil; remove from heat.
Quickly stir in almond extract and flour. Stir vigorously over low heat until mixture forms a ball, about 1 minute; remove from heat.
Add eggs; beat until smooth and glossy. Spread half of the topping over each rectangle.
Bake until topping is crisp and brown, about 1 hour; cool. (Topping will shrink and fall, forming the custardy top).
Powdered Sugar Glaze:
Mix togther powdered sugar, margarine or butter and vanilla.
Stir in warm water, 1 teaspoon at a time, until smooth and of desired consistency.
Assembly:
Spread pastries with powdered sugar glaze; sprinkle with nuts.