The word "flour" conventionally means bleached, all-purpose wheat flour, which is the go-to flour for thickening sauces. “Flour,” however, actually refers to any root, seed or grain milled into a powder. All flours, from wheat to almond to rice, can thicken a sauce, but some do it better than others. Some, such as sweet rice flour, which is milled from short-grain "sticky" rice, are only used for thickening, and make capable substitutions for wheat flour when used in equal amounts. Besides serving as a gluten-free alternative, sweet rice flour has another advantage over wheat flour: it thickens sauces with or without the addition of a fat.
Measure equal parts of whole butter and sweet rice flour or 1 tablespoon each of butter and flour for every cup of sauce you want to thicken, using a gram scale or measuring cups or spoons.
Melt the butter in a saucepan over low heat. Sprinkle the sweet rice flour over the butter while whisking.
Cook the roux until it turns white, blond or brown, depending on the color of sauce you want to thicken, whisking occasionally. White sauces and cream-colored sauces, such as béchamel and veloute, match up best with a white or blonde roux. Dark sauces, such as meat gravies, do best with a brown or dark-brown roux.
Remove the pan from the heat and allow it to cool if you want to reserve the roux for later. Store roux in a sealed food storage container in the fridge for up to three days.
Add the roux to the sauce you want to thicken, using about 2 tablespoons per cup of sauce. You can add warm roux to a cold sauce or cold roux to a warm sauce, but never mix a roux and sauce of the same temperature, as the roux separates and the rice flour congeals to form lumps.
Bring the sauce to a simmer and whisk it vigorously. Simmer the sauce until it reaches the desired thickness and you can’t detect a granular coating on the back of your tongue when you taste it.
Place equal parts whole butter and sweet rice flour in the palm of your hand. Like a roux, it takes about 1 tablespoon each of butter and sweet rice flour to thicken 1 cup of sauce. However, unlike a roux, a beurre manie is intended to thicken and fine-tune the consistency of a sauce at the end of cooking, so you shouldn’t need much.
Work the sweet rice flour and butter into a ball, called a beurre manie, and roll it between your palms until fully incorporated into each other.
Pinch off a small piece of the beurre manie, maybe 1/3 of its total size, and drop it in the sauce while simmering in the last 15 to 20 minutes of cooking. Whisk to incorporate, wait two or three minutes, and check the thickness. Add more beurre manie if needed, a pinch at a time, until the sauce reaches the desired consistency.
Measure 1 tablespoon of sweet rice flour and place it in a bowl with around 1 cup of cold stock, broth or water, while the sauce simmers.
Whisk to combine the liquid and sweet rice flour. Pour the slurry slowly into the simmering slowly while whisking the sauce vigorously.
Stir or whisk the sauce, while simmering, until it reaches the desired consistency.