Add the cream to a medium saucepan and bring to a simmer over medium heat, simmer 30 seconds, until just warm, immediately remove from the heat. Stir in the mint, cover and steep for 15-20 minutes. Using a fine-mesh strainer, strain the cream into a bowl, pressing hard on the mint to squeeze out any cream. Discard the mint. Transfer the cream to the fridge and chill until cold, 1 hour or overnight. In a small bowl, combine the melted white chocolate and sweetened condensed milk until completely smooth and there are no streaks of chocolate. Let cool completely. Using an electric mixer, whip the chilled cream in a large bowl until it forms soft peaks, 3-4 minutes. Add the vanilla, peppermint, and salt and whip until combined. Gently fold in the the white chocolate/condensed milk mixture using a spatula until just combined and smooth. Remove half of the cream and stir in the spirulina (or food coloring), if using, until the cream is pale green. Spoon the green cream into the bowl with white mint cream, gently fold the two together in 2-3 strokes until the cream is swirled. Transfer to a 9x5 inch loaf pan. Cover and freeze until firm, at least 6 hours.Let ice cream sit at room temperature 5–7 minutes, then scoop and enjoy!