For the Cookies:

1. Preheat the oven: Set your oven to 350°F (175°C) and line a baking sheet with parchment paper.

2. Make the dough: Cream together softened butter and sugar in a large bowl until light and fluffy. Beat in the egg and vanilla extract. In a separate bowl, whisk together flour, baking powder, and salt, then gradually add it to the wet ingredients, mixing until dough forms.

3. Chill the dough: Split the dough into two halves, wrap each in plastic wrap, and chill in the refrigerator for at least 30 minutes.

4. Roll out the dough: On a floured surface, roll out dough to about ¼ inch thick. Use a heart-shaped cookie cutter to cut out cookies and place them on the prepared baking sheet.

5. Bake the cookies: Bake for 8-10 minutes, until edges are golden. Let cool for a few minutes on the baking sheet, then transfer to a wire rack to cool completely.

For the Buttercream Roses:

1. Make the buttercream: Beat softened butter on medium speed for 2-3 minutes until smooth. Gradually add powdered sugar, 1 cup at a time, until fully incorporated. Add milk, vanilla extract, and a pinch of salt, then continue beating until fluffy.

2. Add color: Divide buttercream into separate bowls and add food coloring to each for different rose colors. Mix well.

3. Decorate the cookies: Once cooled, use a piping bag fitted with a rose tip (like Wilton 1M) to pipe a rose shape on each cookie. Start at the center and swirl outward in circular motion to form a rose. Repeat for all cookies.

4. Chill and serve: Let the decorated cookies set for 30 minutes to firm up the buttercream before serving.