Mom'S Thumb Cookies
["3/4 c. butter", "1/2 c. sugar", "1 egg yolk, beaten", "1 1/2 c. flour"]
["Mix together butter, sugar and egg yolk; knead in flour. Chill for at least 2 hours.", "Take 1 teaspoon of mixture and roll into a ball.", "Press center with thumb and fill with thick preserves of your choice (strawberry, apricot, etc.).", "Bake at 350\u00b0 for 10 to 15 minutes."]
["butter", "sugar", "egg yolk", "flour"]