Rainbow Chard Soup with Pickled Chard Stems

Name: Rainbow Chard Soup with Pickled Chard Stems
Ingredients: For the Rainbow Chard Soup:; 2 tablespoons unsalted butter; 1 fennel bulb; 10 scallions, roots trimmed, white and light green parts chopped, some dark green parts reserved; 2 garlic cloves, finely chopped; 1/2 jalapeño, stem removed, finely chopped; 7 ounces full-fat coconut milk; 2 1/4 cups water; 1 bunch rainbow chard, stems removed and served, leaves chopped; 1 teaspoon kosher salt, plus more to taste; 1 handful baby spinch leaves; lemon juice; optional toppings: Greek yogurt (or creme fraiche), toasted chopped almonds, toasted coconut flakes, sliced scallion greens, pickled chard stems (recipe below); For the Pickled Chard Stems:; stems from 1 bunch of rainbow chard, ragged ends trimmed; flavorings: fennel frond, fennel seed, garlic, red chile flakes; 1/2 cup white wine vinegar; 1/4 cup water; 1 1/2 tablespoons kosher salt; 1 tablespoon sugar