Line a 15 x 11 x 1-inch jelly-roll pan with waxed paper.
Heat butter in a microwave oven on high for 30 seconds to soften. Mash in large bowl using a wooden spoon. Stir until creamy. Add 1/2 cup of the sugar, stirring carefully, until smooth. Repeat, adding sugar 1/2 cup at a time until about half the sugar is used.
Stir in the milk, 1/4 teaspoon extract and food coloring. Mix until well combined. Stir in the remaining confectioners' sugar, 1/2 cup at a time, mixing completely after each addition. The mixture will come together in a ball.
Lay a large sheet of waxed paper on the work surface. Place candy on paper and flatten slightly into a disk. Cover with another large piece of waxed paper and using a rolling pin, roll candy 1/4-inch thick. Use a 2-inch heart-shaped cookie cutter to cut out hearts. Place on prepared pan. Gather scraps, press together, re-roll and cut into additional hearts until all dough is used.
Let hearts sit, uncovered, for 4 hours or overnight. Turn hearts over.
Blend confectioners' sugar, water and extract until good piping consistency; add 1/4 to 1/2 teaspoon more water to thin slightly, if needed. Write messages or draw designs such as small hearts on each. Let dry thoroughly, at least 5 more hours. Store hearts in an airtight container with waxed paper between layers, at cool room temperature, for up to 1 month. Makes 36 hearts.