Thinly slice your onions.
2 yellow onions
Melt butter and oil into your pot then add the sliced onions.
4 tbsp butter, 1 tbsp oil
Cook over medium heat while stirring until deep brown in color and caramelized. Will take about 30 minutes.
Into the same pot, add tomato paste, curry powder, flour, grate in an apple, and stir while over medium heat for 1 minute.
1½ tbsp tomato paste, ¼ cup curry powder, 2 tbsp flour, 1 apple
Add in your chicken stock, soy sauce, and katsu sauce. Mix to combine and bring it up to a simmer.
1 L chicken stock, 1½ tbsp soy sauce, 1½ tbsp katsu sauce
Using a hand blender, blend everything up until you have a smooth curry.
Add chopped carrots and potatoes into the pot, then cover and keep over medium heat for about 15 minutes or until the potatoes are tender. If the gravy is too thick, add more stock, if it is too thin, just cook longer uncovered. Season with salt and pepper to taste.
2 carrots, 1 russet potato