Heat oven to 350;. Mix shortening, sugar, egg yolk, and vanilla thoroughly. Measure flour by dipping method or by sifting. Blend together flour and salt; stir in. Roll dough into balls (1 tsp per ball). Beat egg white slightly with fork. Dip balls in egg white. Roll in hazelnut finely diced mixture. Place about 1" apart on ungreased baking sheet; press thumb gently in center of each. Bake 10 to 12 min. or until set. Cool. Fill thumbprints with jelly or tinted icing. Makes about 3 doz cookies.
ZoeAnn Hints: These cookies are absolutely melt in the mouth. I use all shortening to minimize spreading too much; however, I find that the use of the crisco with butter flavor really makes a great adaptation. In beating the egg whites, all you want to do is make sure they are thin. If really thick because of their freshness, you might let the egg whites wait overnight in the refrigerator. Of course, leaving at room temperature helps BUT be aware of increased potential food safety problems if left for several hours. Occassionally, the thumbpriints disappear. I carefully punch them down slightly at the point of their maximum "puff" in the oven. The cookies will puff slightly during baking. They should be removed just after "puffing and moistness disappears. Do not overbake. These cookies are suppose to be dainty and so keep them small. Also, when you put jelly on to the thumbprint neatly - not as a big glob. I find that my homemade jams work best. Jellies tend to have more form and don't appear as smooth.
Updated: Monday, June 4, 2012.