1 cup finely ground almonds
2/3 cup sugar
1 egg, lightly beaten
Grated rind of 1/2 lemon
1 1/4 cups flour
1/4 teaspoon salt
1/2 cup butter
3 to 4 tablespoons ice water
1 egg yolk, lightly beaten
Combine the almonds, sugar, egg and lemon rind.
Cover and let the mixture stand overnight.
Place the flour and salt in a bowl.
With a pastry blender or 2 knives, cut the butter into the flour until it resembles coarse meal.
Add the water a little at a time, using only enough to make the mixture stick together. Wrap the dough in waxed paper and chill 1 hour.
Roll the dough out on a floured board into a rectangle. Fold in thirds, wrap in waxed paper and refrigerate 15 minutes. Roll and fold the dough again and refrigerate.
Repeat the rolling and folding 3 more times.
After the last rolling and folding, refrigerate the dough 2 to 3 hours.
Roll the pastry into one - or two - long strips of 4mm thick and 10 centimeters wide.
Mould the almond paste into rolls, 2cm in diameter, about the same length as the pastry.
Place a roll on each pastry strip and brush the edge of the pastry with
beaten egg. Fold pastry round the almond paste and press the seams and ends together very firmly to seal. Turn the roll; the join is now at the bottom.
Form the roll into letters. In Holland, the letters M, S, O and I are traditional and sold in the shops. But it's also nice to make this a personal gift, by twisting the pastry into the initials of the people to whom you plan to give the "boterletter".
Place on a greased baking sheet or on a buttered oven tray. Brush with egg yolk and bake in a preheated oven at 200C (392 F.) for 20 minutes or until golden brown.
Cool on wire rack.