Combine all purpose mix, sugar, 3/4 cup almond flour, and lemon rind.
In a separate bowl, beat butter until soft and fluffy. Add egg yolk and beat well.
Add in the flour mixture and beat until blended. Roll dough into walnut-size balls, then roll balls in egg white and then in remaining 1/4 cup ground almonds.
Place about 2 inches apart on lightly greased cookie sheets. Press thumb into center of each cookie and press any cracked edges back together. Bake at 375°F for 12 to 15 minutes or until lightly browned on edges.
Press tip of a teaspoon into thumbprint to deepen the depression, and fill with a small amount of jam preserves.