Combine the sugar, water, and salt in a small saucepan.
For the sweet cream syrup: Use 1/2 cup heavy whipping cream in place of water.
For the mixed berry syrup: Stir in 1 tablespoon seedless raspberry jam and 1 tablespoon seedless strawberry jam.
Bring to a boil over medium-high heat, and boil for about 5 minutes. Stir to dissolve the sugar, then stir in the vanilla and remove from the heat.
For the mixed berry syrup, stir in the liqueur, if using, and cover the pot. Set aside to steep for at least 2 hours, then strain the syrup.
For the other syrups, set aside to cool. Use the syrup warm or let it stand, covered, until it reaches room temperature.
Syrups will keep, in an airtight container in the refrigerator, for up to 1 week. Reheat in a small saucepan over low heat before using.
Before her diagnosis, Caroline wrote a book on cakes called Cake Magic!. She started developing a birthday cake using her gluten-free mix found in that book. Check out other recipes she’s developing for her new life—and the stories behind them—on her blog, The Wright Recipes. Her next book, Catalan Food, written with chef Daniel Olivella, comes out in early September from Clarkson Potter.