Bubble and Squeak

Name: Bubble and Squeak
Ingredients: 4 tablespoons plus 4 teaspoons unsalted butter , divided; 1/2 large yellow onion , chopped; 1/2 small (about 8 ounces ) green or Savoy cabbage, thinly sliced; 1 bunch (about 8 ounces ) lacinato kale , stemmed and thinly sliced; 1/2 teaspoon salt , plus more to taste; 1/4 cup water; 2 cups leftover mashed potatoes; 1 large carrot , coarsely grated; 1/2 cup chopped parsley , plus more for garnish; 1/8 teaspoon freshly ground black pepper; 4 large eggs; 2 cups halved cherry or grape tomatoes , for garnish (optional)