In a sauce pan on medium to high heat, place the potatoes, salt and water. Bring to a boil, then lower heat to medium and cook until soft. Drain and set aside to cool.
In another sauce pan on medium to high heat, place the marrow as and water. Bring to a boil, then lower heat to medium and cook until soft. Then drain and set aside to cool.
While potato and marrow cool down, in a pan on medium to high heat add oil and sauté the onions until translucent and soft. Remove from heat and let it cool.
In a measuring jug, pour in 250ml warm water and stock cube. Stir to dissolve mixture.
In another measuring jug add 120ml of milk.
To make the soup in a food process add the cooked vegetables and sautéed onions and garlic. Blitz together and then apply pour in the stock bit by bit. Once incorporated pour in the milk bit by bit.
In a large stockpot or saucepan, pour a bit of the mixture into a sieve at a time and push through the soup. This makes the soup extra smooth.
Once all of the mixture has pushed through, on medium heat, heat the soup up. In a measuring jug, pour in 190ml warm water and the remaining stock cube. Stir to dissolve mixture. Pour into the soup mixture and stir well. Now season soup with salt and pepper to taste. Once soup is heated through turn off heat.
In a soup bowl, ladle the soup and serve immediately while pipping hot. Eat as it is or garnish with ground black pepper (optional) and croutons (optional).
