For the hearts, I piped short orange and horizontal lines onto the red icing while the red icing was still wet. Then I dragged a toothpick through those lines, creating the hearts.
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The polkadots are really fun to do! You have to work quickly so the first layer of icing doesn't dry before you finish piping your dots. Use a thinned royal icing to add the orange dots while the red icing is still wet. The dots will settle and spread, creating a smooth, flat surface. For the sort of houndstooth looking one, you pipe orange lines onto the wet red icing, then drag a toothpick through the lines (first from left to right, then right to left).
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The great thing about royal icing is that it looks so smooth, and after you let it dry for a few hours, you can stack your cookies without ruining the icing.
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