In large saucepan, combine chocolate chips, condensed milk and butter, and
cook under low heat.
Stir to mix it together with the potatoes and let the garlic flavour infused with the
potatoes under low heat about a few minutes.
To make the topping, heat olive
oil under low heat, add the walnuts and cook and stir until golden, about 3 minutes.
Combine all the remaining ingredients (except sour cream) and stir into dutch oven — bring up to a
simmer under low heat, stirring constantly, and then increase heat until mixture just begins to boil.
For Bechamel sauce, melt
butter under low heat in a medium saute pan, add flour and cook for about 1 - 2 minutes.
Cook
it under low heat so that it doesn't boil.