In a medium size bowl, cream together the softened butter and sugar until well combined. Stir in the egg and vanilla extract. Then stir in the flour and salt. Cover and chill the dough for 30 minutes.
In a small bowl, use a pastry blender to combine the crumb top ingredients. The mixture should resemble small pebbles.
Divide the dough into 20-22 pieces (dough balls should fit in the palm of your hand). Form a ball, then gently press onto a clean surface so the bottom has a flat edge. Use the underside of a teaspoon or your thumb to create the center well. Dab your finger in water and line the edge or rim of the well center. Gently press the wet edge into the crumb topping. Place on a baking sheet lined with parchment paper or a baking mat and then fill the center with jam or jelly. Repeat for all the cookies.
Bake at 325°F for 12-15 minutes. I like these a little underbaked myself, so I tend to stick to around the 12-minute mark.
You can skip the crumb topping and these are still delicious. But I like the texture and look it creates.