Add the aperol shrub and absinthe into a shaker with ice and shake until chilled.
Strain into a chilled flute, and top with the chilled cava.
Garnish with an orange twist.
*Grapefruit shrub: Combine 2 cups sugar, 2 ½ cups grapefruit juice, 1 cup apple cider, a pinch of salt and the zest of the juiced grapefruits in a saucepan. Simmer ingredients over medium heat, stirring for about 20 minutes. Remove from the heat, strain out solids, let cool, and store in the refrigerator.