In Japan, the most common way of making curry sauce (and thus curry rice) is to chop up your ingredients (often carrots, onion, and some form of potato or tuber, perhaps a little meat), saute them in some fat, then add water and some roux blocks (think of House or S&B) and cook until the sauce forms. Lots of folks still make their own from the way things appear, or else S&B probably wouldn't bother to continue producing a tinned curry powder.
Because of the Wife's foresight in purchasing large quantities of Tamanishiki Gold brand rice, we've got lots of high quality short-grain rice on hand. It's truly convenient to have our main starch just sitting in the pantry, not having to worry for two months at a stretch about running out (like we used to with bread). The one thing we were sadly missing was tsukemono to serve the curry rice with. Traditionally and taste-wise curry rice gets served with fukujinzuke or pickled rakkyo. I haven't tried it yet, but I suspect that it would go well with curry udon as well.
The recipe I use is adapted and tweaked from a translated article about the Imperial Japanese Navy's traditional form of curry served since before World War II. It was an expedient way to rid the galley of excess carrots, potatoes, onions and beef, and became a hallmark of their food services. Originally, the cooks made it more oily and thin than modern curry sauce (and I'd bet they did it to stretch the ingredients out).
The first time the wife and I tried going directly from the recipe, there was a large amount of excess fat to skim off of the surface. Since them, I've cut my recipe down in a lot of ways, and made it an ideal way to make dinner for four to six people. It keeps at least a week in the fridge if you seal it up nice and tightly.
Fortunately, you can profit from our mistakes and trials. If you need to make something gluten-free, I usually use rice flour (mochiko) and potato starch in a 4:1 ratio to replace wheat flour in gravies like this. Give it a shot - this is one of those times where gluten-free cooking doesn't leave some texture or flavor to be desired!
4 Tbsp Curry powder
2 Tbsp Rice flour
1/2 Tbsp Corn or Potato starch
4 Tbsp Lard
32 oz. Beef Stock
2 Lg Carrots, peeled and sliced
1 Med Potato, peeled and cubed
1 Sm Onion, peeled and diced
1 Tbsp Butter
OPTIONAL -1/2 Lb Meat (I prefer pork, any land animal will do!)
In a 1 quart sauce pan, melt the lard on medium high heat. Combine all the dry ingredients of the curry sauce and add to the melted lard. Stir and cook until it forms a thick paste, adding additional flour if needed. Set aside.
In a medium stock pot, melt the butter over high heat. Saute onions and carrots briefly, then add the potatoes and any meat. Continue to saute until ingredients are mostly cooked. When the onions are translucent, add all beef stock and bring to a boil. Add the curry roux and stir to combine. Bring close to a boil to thicken, then lower heat to medium-low and stir occasionally.
Serve over rice (count on needing 1/2 cup uncooked rice per person at a minimum) or udon (1 bundle per person).