Heat olive oil in a saucepan over medium heat and sauté minced onion until softened.
Add garlic, sweet pimentón, and hot pimentón, stirring for 30 seconds.
Whisk in tomato paste and flour, cooking for 1 minute.
Slowly pour in vegetable stock while whisking constantly to prevent lumps.
Simmer the sauce for 10-12 minutes until thickened, then set aside.
Heat frying oil in a deep pot to 160°C.
Par-fry potato cubes for 6 minutes until tender but pale.
Remove potatoes and increase oil temperature to 190°C.
Fry potatoes again for 3 minutes until golden brown and crispy.
Drain on paper towels, season with salt, and serve topped with the warm sauce.