Shepherd's Pie with Vegetables and Sweet Potato Puree

First, peel the white potatoes and sweet potatoes, cut them into cubes, and place them in a large pot. Cover them with water and bring to a boil over high heat. Meanwhile, peel the onion and garlic; finely chop the onion and crush the garlic. When the water starts to boil, reduce the heat to medium and cook the potatoes for 15-20 minutes, until tender.

Once the potatoes are cooked, drain the water, add the milk and salt, then mash everything until you get a smooth and homogeneous puree.

Meanwhile, clean the mushrooms and cut them into small pieces (approximately the size of beans). Drain and rinse the red beans and lentils under cold running water.