Vegetarian Shepherds Pie

Name: Vegetarian Shepherd's Pie
Ingredients: 2 tablespoons extra-virgin olive oil; 1 large onion, finely diced; 2 carrots, peeled and thinly sliced; 2 celery stalks, thinly sliced; 10 ounces cremini mushrooms, trimmed and sliced; 1 tablespoon tomato paste; 1 tablespoon vegetarian Worcestershire sauce, such as Annie's Naturals; 1 dried bay leaf; 1 cup French green lentils, picked over; Kosher salt and freshly ground pepper; 1 cup frozen peas; 2 pounds Yukon Gold potatoes, scrubbed and cut into 1 ½-inch pieces; 4 cloves garlic; 4 tablespoons unsalted butter; ½ cup whole milk, warmed