The starch in flour works to thicken sauces, giving them a consistency perfect for drizzling. However, other starch-based products, such as matzo, also known as matzah or matzoh, can work as an alternative. Matzo bread, a kosher unleavened bread using flour that is grown and processed according to Jewish religious tenants, is ground to create a flour. Available in most grocery stores, the flour can be substituted for regular all-purpose flour in a 1-to-1 ratio. Use in the typical manner to thicken gravy, whether through a slurry or a roux.
Slurry
Whisk matzoh flour with cold water to make a slurry, generally in a ratio of 1 tablespoon with 1/4 cup of cold water for a small amount of gravy. Heat the liquid for the a gravy in a saucepan on the stove, whether stock or drippings from a roast. Add the slurry to the hot liquid, whisking as it is drizzled in. Continue to whisk over medium-high heat as the mixture simmers, until it is thickened to your preferred consistency.
Roux
Combine an equal part of flour and oil or butter -- generally 2 tablespoons of the matzo flour with 2 tablespoons of oil. Place in a saucepan and turn to medium-high heat. Continuously stirring, fry the matzo flour until a light golden brown color. Add small amounts of the liquid you're using for the gravy, such as chicken stock, a 1/2 cup at a time until the mixture resembles a thick liquid. Continue to add stock or drippings until the gravy is at the desired consistency.
Considerations
Season the gravy with salt after it is as thick as you like it. Simmer the liquid with desired herbs and spices before thickening it, as this will add more flavor than if they were simmered after the mixture was thickened. Create matzo meal from the whole pieces of matzo by crumbling them into a coarse mixture in a food processor and blending on high, pulsing the mixture, for several minutes.
Alternatives
Use the typical alternatives to all-purpose wheat flour when substituting for matzo flour. Corn starch, combined with cold water, can be added to hot stock or drippings to create gravy. Use 1 tablespoon for every cup of liquid thickened. For a kosher alternative, use potato starch, preparing it in the same manner and using the same ratio as corn starch before adding to a hot liquid.