Sauté the garlic, pistachios, fennel seed, and dulse in 2 tablespoons of butter over medium heat until the garlic is no longer raw and the nuts and seeds are toasted, about 3 minutes. Stir to combine and remove from the heat. Let cool slightly. Add the remaining butter, lemon juice, and mint. Season with salt, and stir to combine. Set aside until ready to use. It will last a week or more in the refrigerator.