Elderflower cordial is a sweet mixture with a distinctive floral fragrance. Elderflower cordial comes from the elderflower of Europe and can be bought at speciality liquor stores or on the Internet, but if you cannot find it, other ingredients will substitute for it in recipes.
Elderflower cordial is noted by "The Nibble" to have notes of lychee flavour. Lychee liqueur, while not an exact match, can replace elderflower cordial in recipes when a fruity, floral drink is needed.
Citrusy Grand Marnier is often the liqueur Elderflower cordial replaces in recipes, so it should stand that the replacement goes both ways. Substitute an equal amount of Grand Marnier for Elderflower cordial in your recipes for food and drinks. The citric acid in elderflower cordial makes Grand Marnier a comparable substitute.
If you have time, make your own elderflower cordial overnight. Recipes for this abound on the Internet, but you will have to find your own source of fresh elderflowers. Ideally, you have them growing in your yard. They are bright white flowers. Be sure to only use those grown without pesticides. The basic recipe calls for steeping elderflowers in sugar syrup with lemon slices and citric acid overnight. The mixture is then strained and diluted with club soda for serving.
Replace elderflower cordial with an equal amount of a fruit liqueur such as black current liqueur or apple liqueur. These mimic the fruity flavours in elderflower cordial. Black current liqueur and apple liqueur are often more readily available in liquor stores than elderflower cordial.
Elderberry Flower Drink Syrup
In international markets, look for elderberry flower drink syrup. This is a sweet infusion of elderflowers with sugar. It can be mixed with gin and tonic or with club soda for a summer drink alternative to lemonade. If you cannot find this in international markets, look on the Internet for this syrup. Replace elderflower cordial with the syrup on a one to one basis in your recipes.