variety of oatmeal thumbprint cookies

i baked a batch of oatmeal thumbprint cookies. i think the end total was about 3.5 dozen bite size cookies. the first dozen i baked followed the recipe minus the walnuts and i used peanut butter and strawberry preserves for the topping. the second dozen followed the recipe with the walnuts using prickly pear jelly melinda had made and the remainder of the cookies followed the recipe minus the walnuts, also with the prickly pear jelly. these cookies taste really buttery and i liked the way all the batches came out, but i think i enjoyed the original recipe with the walnuts the best.

1 cup (1/2 lb.) butter, at room temperature

1/2 cup firmly packed brown sugar

1 large egg, separated

1 1/2 teaspoons vanilla

1 cup all-purpose flour

2 cups rolled oats

1 1/2 cups finely chopped walnuts

About 1 cup fruit jam

Preparation

1. In a bowl, with an electric mixer on high speed, beat butter, brown sugar, egg yolk, and vanilla until smooth. Stir or beat in flour and oats until well blended.

2. In a small bowl, beat egg white and 2 teaspoons water to blend. Put walnuts in a shallow bowl. Shape dough into 2-teaspoon-size balls and dip in egg white mixture; shake off excess, then roll in walnuts. Place 1 inch apart on buttered or cooking parchment-lined 12- by 15-inch baking sheets. Press your thumb into the center of each cookie to make a 1/2-inch-deep indentation.

3. Bake cookies in a 300° oven until lightly browned, about 15 minutes; if baking more than one pan at a time, switch pan positions halfway through baking.

4. Carefully fill each indentation with about 1 teaspoon jam (if indentations have disappeared, make them again with the rounded end of a wooden spoon). Return to oven and bake until cookies are golden brown and jam has melted, about 15 minutes longer. With a wide spatula, transfer cookies to racks to cool