Clean the leek by slicing into it lengthwise and gently rinsing under running water. Cut the leek into thin slices and place into a large mixing bowl.
Peel and grate 3-4 potatoes depending on their size to get 3 loose cups. If the grated potatoes are super juicy, wrap in kitchen towel and pat dry to absorb excess liquid. Add to leeks.
Add 3 tablespoons flour, garlic powder, salt and pepper, and 2 tablespoons milk to the potatoes. Toss to incorporate. The potatoes will be coated and sticky (see photo). Add more flour/milk if needed to get a sticky mixture.
Heat ~½ inch of oil in a heavy bottom skillet over medium-high heat until shimmering. Once hot, place scant ¼ cup of potato mixture into the skillet and let it fry until crispy and brown. Flip it (the second side does not take as long to cook). Around 6 - 8 minutes total.
Place on paper towel to absorb any excess oil.
PRO TIPS: Depending on how big your pancake is and how hot your stove runs, you may have to adjust your heat (don't go too hot or they burn on the outside and are raw on the inside). Start at medium to medium-hot and then reduce heat as needed.