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

In a mixing bowl, combine the flour, baking powder, and salt, whisking them together until well blended.

In another bowl, beat the softened butter and brown sugar together until creamy and light in texture.

Incorporate the egg and vanilla extract, mixing until fully integrated.

Slowly introduce the dry ingredients into the butter mixture, stirring until just combined.

Add the ground cinnamon and milk, mixing until the dough is smooth and cohesive.

Take spoonfuls of the dough and roll them into balls, placing them on the prepared baking sheet with enough space between each.

Using your palm or the bottom of a glass, gently press down on each ball to flatten them slightly.

Bake for about 10-12 minutes, or until the edges turn a light golden brown.

Allow the cookies to cool on the sheet for 5 minutes before moving them to a wire rack to cool completely.

For the icing, combine the powdered sugar with 1-2 tablespoons of milk in a small bowl, stirring until you achieve a smooth consistency.

Drizzle the icing over the cooled cookies and sprinkle with colorful decorations if desired.