Preheat and Prepare:

• Preheat your oven to 350°F (175°C).
• Line a baking sheet with parchment paper.

Make the Cookie Dough:

• In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.
• Add the egg and vanilla extract, beating well to combine.
• In another bowl, whisk together the flour, baking powder, and salt.
• Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Shape the Cookies:

• Roll the dough into 1-inch balls and place them on the prepared baking sheet.
• Using your thumb, make an indentation in the center of each ball.

Add the Jam:

• Fill each indentation with a small spoonful of berry jam.

Bake:

• Bake in the preheated oven for 10-12 minutes or until the edges are lightly golden.
• Remove from oven and let cool on the baking sheet for a few minutes before transferring to a wire rack.

Prepare the Frosting:

• In a small bowl, mix together the powdered sugar and milk until smooth.
• Add a few drops of food coloring if desired, achieving your preferred shade.
• Spoon or pipe the frosting over cooled cookies, covering the jam.

Finish and Serve:

• Garnish with coarse sugar crystals.
• Allow the frosting to set before serving.