Preheat oven to 350 degrees F (175 degrees C). Grease cookie sheets.
In a large bowl, cream together the butter, sugar, eggs, and vanilla until light and fluffy.
In a separate bowl, mix together the flour, baking powder, and salt. Gradually add the flour mixture to the creamed mixture, stirring until well blended.
Roll the dough into 1-inch balls and place on the prepared cookie sheets. Make an indentation in the center of each cookie using your thumb. Fill the indentations with jelly.
Bake for 10 to 12 minutes in the preheated oven, until lightly browned.
Interesting Facts
Jelly cookies are also called thumbprint cookies because of the indentation made on each cookie.
Jelly cookies can be made with any type of jelly or jam.
You can also add sprinkles to the jelly in the center of each cookie for an extra burst of color.