Gradually add sugar, and cream until light and fluffy.
Beat in egg yolk, vanilla and flour, blend thoroughly.
Roll into walnut-sized balls and place on greased cookie sheet.
Make a nice indentation in top of each cookie, I use the end (the handle end)of a wooden spoon for this.
Put a little bit of jelly or jam into each indentation.
Bake in 350º oven for at least 15 minutes or til pale golden yellow.
Cool, then sift powdered sugar over them.
*Tips for measuring four!
When recipes say "flour, sifted", it means to measure the flour into a sifter, then sift into the rest of the ingredients.
When a recipe says "sifted flour", that means that you sift flour into a separate bowl first, then measure it, then add to the rest of the ingredients. In this recipe, if you don't sift the flour first, you will be adding too much, and your dough will be a little dry and hard to work with.
Also, lightly spoon your flour into your measuring cup, don't scoop it from the bag or your bowl. Scooping it compacts the flour and you will be adding too much whether it has been sifted first or not. (Then always level it off with the straight edge of a knife.).
Some recipes are "forgiving", but baking recipes aren't always that forgiving! Correct measuring can be extremely important.