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Add the butter to a small skillet. Heat over medium on the stove, stirring occasionally, until the butter has completely melted.  To save time, you can skip over the instructions for making your own curry roux and use premade commercial curry cubes, instead. You will need about 4 cubes, or 3.5 oz (100 g), to match the amount of curry roux used in this recipe. Add them to the curry when you would usually add the homemade roux.  Do not melt the butter on a higher heat setting. Butter has a tendency to flash-boil once it reaches its smoking point. If you allow this to happen, you could cause the hot sizzling butter the splatter. The fat in the butter may also begin to break down, thereby affecting the flavor of the curry roux. Sprinkle the flour into the melted butter. Quickly stir it into the butter and continue cooking for 15 to 20 minutes, or until the roux turns a deep tan color.  You must stir the roux constantly as it cooks, at least until the butter and flour fuse together and begin to swell. After that point, continue to stir the roux frequently. If you fail to stir the roux enough, it will burn quite quickly and develop a bad taste. The flour must be allowed to cook thoroughly in this manner. If you do not cook the flour enough, it will retain a strong starchy taste. Sprinkle the curry powder and garam masala into the roux. Stir the ingredients into the roux over the heat for about 30 seconds. Remove the roux from the heat as soon as the roux is seasoned. You'll know that the spices have mixed into the roux once they release a strong aroma. Remove roughly 1/2 to 1 cup (125 to 250 ml) of the cooking liquid from the curry base. Rapidly stir this liquid into the roux until a paste forms. Add a little of the liquid first and mix it in gradually. You only want to use the minimum amount necessary to form a paste. If you add too much at once, combining the liquid with the roux might become difficult.
Melt the butter in a separate skillet. Add the flour. Add the spices. Ladle cooking liquid into the roux.