Preheat oven to 350 degrees. Line regular or miniature cupcake pans with liners; set aside. In a mixing bowl, whisk together flour, baking powder, and salt; set aside.
In a large mixing bowl, cream butter and sugar until light and fluffy, about 5 minutes. Add eggs one at a time, beating well after each addition. Scrape down bowl, and beat in vanilla.
Alternating, add flour mixture and milk to butter mixture, beginning and ending with flour. Scrape sides and bottom of bowl to ensure batter is thoroughly mixed.
Divide batter evenly among liners; fill regular pans three-quarters full and miniature pans to just below the top. Bake until golden and tops spring back when lightly pressed, about 20 minutes for regular and 15 minutes for miniature. Rotate pans once while baking. Turn out, and transfer to a wire rack. Let cool completely.
Fill pastry bags fitted with couplers with buttercream. To shape the petals: Use an Ateco #104 flat-petal tip. With the wide edge of the tip in the center of the cupcake, pipe the petal by making a halfmoon motion with the outer, thinner edge of the tip. Repeat until you have 5 or 6 petals forming a flower. Garnish the center with a candy. To shape the leaves: Use an Ateco #68 leaf tip with green icing to make the leaves by piping from the flower towards the edge of the cupcake, lifting off as you reach the end. Place iced cupcakes in refrigerator until ready to serve.
Unfrosted cupcakes can be made ahead of time and stored in an airtight container at room temperature a day ahead, or frozen up to three weeks.