01 - Cook the spaghetti in a large pot of salted boiling water according to package directions. Drain, reserving 2 tablespoons of pasta water. Set aside.
02 - Combine blueberries, lemon juice, honey (or agave), and salt in a saucepan over medium heat. Cook for 5-7 minutes, stirring and gently crushing berries until juices are released.
03 - Add heavy cream and lemon zest to the blueberry mixture. Simmer for 3-4 minutes, stirring until the sauce slightly thickens.
04 - Remove from heat. Blend the sauce until smooth using an immersion blender or a standard blender.
05 - Stir the tonic water and reserved pasta water into the blended sauce.
06 - Toss the cooked spaghetti with the blueberry sauce until evenly coated.
07 - Plate the pasta. Garnish with crumbled feta cheese, torn basil leaves, and optional edible glitter or neon food coloring. Serve immediately.
08 - For optimal glow, place the finished dish under a UV blacklight before serving.