Combine all ingredients in a large bowl. Beat with an electric mixer at low speed until combined. Beat on high 8 to 10 minutes or until stiff peaks form.
*Meringue powder is available at specialty food shops, cake decorator supply houses, crafts stores, and some supermarkets.
Royal icing tips:
Store icing in a glass or metal container; it will break down in plastic.
Reserve a set of pastry bags, couplers, and tips exclusively for royal icing. (Your old cake-decorating bags may not be grease-free.) Disposable pastry bags or parchment triangles rolled into cones will work. Store filled pastry bag tip-down in mug with damp paper towels in bottom. Seal top with twist-tie or rubber band, and drape with plastic wrap.
Keep bowl of icing covered with damp paper towels and plastic wrap at all times. Uncovered, it will harden like concrete.
More decorating ideas:
Chimneys: Chocolate rock candy; gum paste for stonework; nuts of varying size, shape, and color.
Lakes, ponds, and streams: Melted, crushed hard blue candy. Technique: Place crushed candy on foil, and bake at 275° for 3 to 4 minutes. (Watch carefully!) Let cool, and peel off foil.
Lampposts: Stick candy; candy canes (for Christmas).
Lawns: Flaked or shredded coconut tinted green and "planted" in green royal icing.
Paths and walkways: Brown or raw sugar (for sandy paths); couscous; nonpareils; crushed chocolate jimmies; broken brown or gray Necco wafers; gingerbread shaped into cobblestones.
Roofing: Sliced almonds; pecan halves; chewing gum cut into "shingles"; graham crackers; mini shredded whole wheat cereal pieces (for thatch); crispy wheat cereal squares; jelly beans, candy-coated chocolate pieces, red cinnamon candies, silver dragées, licorice laces.
Shutters: Chewing gum, licorice sticks.
Window panes: Sheet gelatin (for clear windows); crushed colored hard candies (for stained glass). Technique: Fill window cut-outs in half-baked gingerbread pieces with crushed candy; return to oven, and bake at 350° for 7 to 8 minutes until melted. Let cool to room temperature.
Woodpiles: Tootsie Rolls, pretzel sticks, breadsticks.