Suet is my new favorite fat. It is, for reasons baffling to me, the least known of all the animal fats we use in our kitchens. Its porcine equivalent is leaf lard, the cylindrical mass of fat surrounding the kidneys of the pig; suet is the term we use for the fat surrounding the kidneys of cows.
For most of my life, I've been a lard and duck fat user. But as autumn began and I started baking again, I had an epiphanic realization about suet: unlike pork and poultry fat, you don't need to render suet in order to use it in your pastries. No standing over a pot and waiting for your cubes of animal fat to turn into liquid (and then resolidify) is required when it comes to suet. This means that you could keep a large chunk of suet in your freezer and take it out at a moment's notice when you feel like making a pie or whipping up some biscuits to go with your meat and gravy. Think about that, fat lovers.
Suet owes its versatility to its texture: it is the firmest of all the animal fats we use for cooking and possesses the highest melting point. Even at room temperature, suet stays solid and hard. Unrendered leaf lard, if you leave it sitting on your counter for even a little while, will turn greasy and waxy as it softens. Unrendered suet, on the other hand, is so firm that you have plenty of time to roll out and shape the dough without worrying about the fat prematurely melting into the flour.
When used in pie crusts, suet gives you a flaky and crispy texture that stands up well to wet filling. Suet's flavor profile is clean and not particularly beefy; though lard gives you a slightly sweeter flavor, suet's hardness more than compensates for its blander taste. A combination of butter (that other miraculous fat from ruminants) and suet gives both the flavor and texture desirable for pie crusts, though if you were baking a rustic meat pie, using suet exclusively would be more than satisfactory.
For biscuits, suet yields a tender crumb and depending on the fineness which which you cut the fat, the interior texture of the biscuit ranges from fluffy to dense. Grating the fat and mixing it with the flour gives you a fluffy, light biscuit. If, instead of finely grating the fat, you rub it to a coarse cornmeal consistency with your fingers, you'll end up with a biscuit that's a cross between crisp crust on the outside and tender, foccacia-like bread inside.