Grapefruit Sabayon Cakes - SippitySup

Ingredients

• 1 tablespoon unsalted butter, at room temperature
• 3 large eggs
• ½ cup granulated sugar
• 2 tablespoons all-purpose flour
• 2 teaspoons red grapefruit zest
• ¼ cup freshly squeezed red grapefruit juice
• 1 cup whole milk
• 1 pinch kosher salt
• 2 tablespoons confectioners sugar
• 3 cups boiling water, or more as needed