Begin by preheating your oven to 350°F. In a mixing bowl, cream together the softened butter and sugar until the mixture is light and fluffy. Incorporate the egg yolk and mix thoroughly. Gradually add the all-purpose flour, stirring by hand until the ingredients are well combined.

On a lightly floured surface, gently knead the dough for 2 to 3 minutes until it is uniform in texture. Shape the dough into 1-inch balls and arrange them on greased baking sheets, leaving a 2-inch space between each cookie. Utilize the end of a wooden spoon handle to create an indentation in the center of each ball, and fill this well with approximately 1/4 teaspoon of your chosen fruit preserves.

Bake the cookies for 13 to 15 minutes, or until the edges are lightly browned. Once baked, transfer them to wire racks for cooling. If desired, dust the warm cookies with confectioners' sugar before serving.