Preheat your oven to 350°F (175°C) and line your baking sheets with parchment paper.

In a mixing bowl, beat the softened butter and light brown sugar until light and fluffy for about 2-3 minutes.

Add the egg and teaspoon of vanilla extract, mixing until fully combined.

In another bowl, whisk together the all-purpose flour and salt, then gradually add this mixture to the butter mixture, combining gently.

Roll the dough into balls, about one inch in diameter, and place them on the baking sheets with space in between.

Make a small indentation in the center of each ball using your thumb or a spoon.

Bake the cookies for 10 to 12 minutes, just until the edges start to turn golden.

Allow to cool on the baking sheets for a few minutes before transferring to a cooling rack.

In a small saucepan over medium heat, combine cubed butter, sugar, evaporated milk, and vanilla extract.

Stir continuously until boiling, then let it simmer for 2 minutes.

Remove from heat and stir in food coloring to achieve desired colors.

Once cookies are cooled, fill each indentation with the colored filling.

Optionally decorate with colored sprinkles.