Finally, the secret to these delicious crispy Belgian fries! Actually, it comes down to two things: the fat and a two-step cooking process.

Important
Belgian fries are always washed a number of times in fresh water; no Belgian would forego this essential step. Generally they're washed two or three times, but if you let them soak in water for 30 to 60 minutes, they're even better. It's only once they've been well washed and well dried with a towel that the real fry preparation begins. 

Secondly, it's important that the fries be square and equal in size so that the cooking is even on every side. 

Hints and tips
It's best to prepare the fries 1 or 2 portions at a time so that they're not overcrowded in the frying oil. 

1. Peel the potatoes; wash them to remove any  particles of dirt or peel and pat dry (see note above);
2. slice each potato into 12 mm (1/2") thick sticks; pat dry again; 
3. drop the fries into hot beef fat at 160° (325° F) - easy if you're using an electric deep fryer. Fry for 6-7 minutes; drain and let rest for 5-10 minutes;
4. meanwhile, increase the heat to 175° C (350° F) and fry the fries again until crisp and golden.