Diced potatoes fried in butter and duck fat

Well yes, just fried potatoes. It's a simple sidedish, but who does not like crispy golden potatoes?
The three tricks to achieve this crispiness are as follows:
1) Potatoes should be fried twice - first on medium heat until nearly done and after that on high heat until ready - just the way you prepare chips. This two-steps process creates crunchy golden crust and buttery inner core of the potato dices.  
2) You "prepare" the potatoes before frying by putting them in a bowl with 1 Tablespoon sea salt dissolved in cold water enough to cover them. The salt from the water will drain the liquids from the potatoes.
3) You put the potatoes in hot oil. The high temperature will seal their surface and will not allow them to absorb much fat.
Using the duck fat as an ingredient in this recipe is very optional. It has a special aroma which will not be everybody's favourite, but if you like its rich flavour, it will make the potatoes even crispier. 

Ingredients:

• 5 medium potatoes
• 3 Tbsp olive oil
• 3 Tbsp duck fat (if you don't have or don't like, use butter again)
• 2 Tbsp butter
• salt

Preparation:

Peel, wash and cut the potatoes into small cubes. Put them in a bowl with 1 Tablespoon of salt dissolved in cold water and let them in the water about 20 minutes. Put them on a dishcloth to remove the liquid from them. Heat olive oil and butter and add the potatoes. Cook 15 minutes on medium heat stirring occasionally until potatoes get light brown. Remove them from the pan, rise the heat to high and add the duck fat. Bring potatoes back to the pan and fry for additional 5 minutes until golden brown. Season with salt.