1Preheat oven to 300 degrees F (150 degrees C). Grease 2 baking sheets or line them with parchment paper.
2Separate the egg, reserving the egg white. Mix the butter and brown sugar; beat in the egg yolk. Stir in the vanilla. Mix in the flour and salt, stirring until well blended.
3Lightly beat the egg white.
4Shape the dough into balls. Roll in beaten egg white, then nuts. Place the cookies on the baking sheets about 2 inches apart. Bake in the preheated oven for 5 minutes.
5Remove cookies from oven. With thumb, dent each cookie. Put jelly or preserves in each thumbprint. Bake for another 8 minutes.
Footnotes
Cook's Note:
I like to use seedless raspberry jam, as well as apricot preserves.