Place 2 teaspoons chopped basil in each prepared Assam Tartlet Shell.
In a large skillet, heat butter and oil over medium heat. Add onion and garlic; cook until onion softens, approximately 5 minutes. Add mushrooms, sweet potato, carrot, and zucchini; cook until sweet potato is still somewhat firm, 2 to 3 minutes. Add salt and pepper, stirring well. Remove vegetable mixture from heat. Add remaining ¾ cup basil, stirring well.
Divide vegetable mixture among prepared tartlet shells. Sprinkle each tartlet with goat cheese.
In a small bowl, whisk together milk, cream, and egg. Pour over vegetables.
Bake tartlets until shells are golden and custards are set, 15 to 20 minutes. Let cool for 10 minutes before serving. Serve warm or at room temperature.
Recipe by TeaTime Magazine at https://teatimemagazine.com/assam-vegetable-tartlets/