In a bowl whisk together flour, salt, and baking soda. In another bowl whisk together peanut butter, butter, and brown sugar until smooth and whisk in egg and vanilla. Add flour mixture to peanut butter mixture, stirring until blended.
Roll pieces of dough into 1-inch balls and roll in granulated sugar. On a large baking sheet arrange balls 2 inches apart and bake in middle of oven 10 minutes. Working quickly, with the back of a 1/4 teaspoon measuring spoon make an indentation about 1/2 inch in diameter in center of each cookie. Fill each indentation with slightly heaping 1/4 teaspoon jelly and bake cookies 10 minutes more, or until golden. Transfer cookies to racks to cool.
