Place the beetroot in a saucepan, cover with water, add salt, pepper and bay leaf and bring to a simmer. Simmer until tender, about 1 hour. Towards the end of the cooking time, add the stock cube. Puree the soup.
In the meantime, make the tortellini. In a bowl, combine flour, egg, oil and water. Knead to make a smooth dough.
Brown the mince in a frying pan and season with salt and pepper.
Roll out the dough until very thin and cut into 4cm squares. Place a little mince in the centre of each square and fold into a triangle. Fold down the tip and then stick together the two corners at the base of the triangle.
Cook the tortellini in boiling salted water until they float and serve in the beetroot soup.