Most of the designs require piping colors onto wet frosting. I recommend working in small batches and flooding 2-3 cookies at a time with white frosting, then piping the designs on, then doing another small batch, to avoid having the royal icing dry out before the cookies are fully decorated.
To flood the cookies, fit a piping bag with a small round tip (I recommend a #2 tip) and fill it with white frosting. Draw a thin outline with the royal icing around the outside of a few cookies. Next fill the center of the cookie with royal icing. If you miss any spots, use the tip of the piping bag to nudge the icing into place, or use a toothpick to smooth out any rough lines. This is your blank canvas for making all the Valentine’s Day designs! Make sure to work quickly to decorate the cookies after they have been flooded.
To make heart outline cookies: pipe dots of color along the outer edge of the cookie, spacing them about ½-inch apart. The dots should sink into the wet white icing fairly quickly. Take a toothpick and, starting at the top center of the heart, drag it through the line of colored dots. The dragging motion will create an elongated heart shape in each dot. You can also pipe randomly placed dots all over the cookie, and drag a toothpick through the dots individually to make hearts.
To make zigzag cookies: pipe lines of alternating colors horizontally across the white icing. Take a toothpick and drag it through the lines vertically. Once at the bottom of the cookie, move the toothpick over a little bit (perhaps 1/8”) and drag it upwards, creating a zig-zag in the opposite direction. Continue this pattern until you’ve created lines across the whole cookie.
To make elegant rose cookies: these look best when made with two different shades of the same color, like pale pink and dark pink. Start with the pale pink and pipe several blobs on top of the cookie—refer to the picture tutorial to get a general idea of the shape. Take the darker pink color and pipe a line across the center of the blob. Finally, add a dot of white in the center. Now for the fun part! Take a toothpick and start swirling the colors together. It should only take a few swirls before they start to look like abstract roses. Add a few dots of green around the edges, and pull the dots of green out with a toothpick so they look like leaves.
To pipe stiff rosettes on cookies: the rosettes can be piped onto plain white cookies, or cookies that have been decorated with dots, stripes, or whatever else you like. Let the base cookies sit and dry for about an hour before adding the rosettes on top. Place stiff consistency frosting in a piping bag fitted with a small star tip. Start in the center and pipe a small swirl outward in a rosette shape. You can do just 1 flower or several bunched together. Decorate the edges with small leaves piped with stiff green frosting, if desired.
The decorated cookies can be enjoyed the same day they are made, but the royal icing will probably take 8-12 hours to fully dry, so if you want to stack and store them, let them sit at room temperature overnight to dry and harden before packaging them.