Pour the two kinds of milk into a large saucepan on low heat and stir with a spatula until it thickens. Stir constantly or the milk will stick to the bottom and burn.
You want the mix to be really thick in the saucepan, like cooled-down manjar blanco or dulce de leche. Then, out of the saucepan it will thicken even more as it cools.
Remove it from the saucepan and let it cool down completely. Then, freeze the mix for at least 4 hours or up to 3 months.
With the help of a teaspoon, remove a portion of the manjar blanco and form a ball with lightly greased hands.