Add the orange juice and curaçao to a champagne flute. Top up with your sparkling wine and garnish with an orange slice if desired.
I like to use freshly squeezed orange juice, but a high quality (not from concentrate) store-bought OJ will do in a pinch. The addition of a little triple sec will help bring out the orange flavor in your cocktail.
Use a sparkling wine you don't mind drinking on its own, but save your fancy Champagne for another occasion. I like to use a Spanish Cava or an American sparkling wine to get the most value for my money.