There are several suet recipes for birds and much debate about what should or should not be included with respect to fats. In general it it best to not use bacon grease. Birds cannot metabolize salt and sure nitrates are no good for them nor for us. That's a fact, not opinion. Hydrogenated fats (shortenings) could have similar argument against them. I do not use them.
Beyond those two no-no's (no hydrogenated or nitrate/salt fats) there are lots of alternatives. I make my suet using lard/peanut butter with a mixture of 2:1 cornmeal flour. I sprinkle in ground egg shells. To the flour mixture I add enough lard to create a dough-like mixture. You can use your food processor or stand mixture to accomplish this as well. If using the food processor, just add the lard unmelted. I found the stand mixer or hand mixing works better with the lard melted.
Lard can be expensive. I look for it at my local salvage store where I can get it for .99 per 1lb tub. My Restaurant supply store used to sell 38lb buckets, which I think was less than $20, but they stopped carrying it. I have purchased 50lb box (which costs alot to ship) but it is still cheaper than buying from the grocery store. So if my local salvage place has it for .99, I get it!
I buy cornmeal by the 50lb bag and the restaurant supply store. It costs less than $20. You can use it for the birds and for your own consumption! I also get my flour there too and substantial discount. I've been out of that large bag of cornmeal for a while. With COVID, I carefully manage my exposures. I have a 50lb bag of cracked corn. It costs less than $10. Hmmm! I pulled out my Blendtec and inside of a minute it was ground perfectly for suet. That, now, is my low cost means of producing cornmeal for my suet.
I will warn you....once you start making suet, you can never stop. Your customers will show up, eat everything up and beg for more. Yep. In the wee hours of the morning they will be queued up waiting for bounty to arrive.
I put my suet in a rat wire cylinder. It keeps the squirrels from absconding with large chunks of suet. They will still get at it, and you will realize how long a squirrel's tongue is as they lap at the suet from the wire. Rat wire also has the ability to conform to crooks of trees and such. But if you are not handy (or don't have) basic wire cutting tools, that mode is not for you. You can buy the green wire cages to put your suet in. They are long lasting.. I put mine on a baking tray or silicone mat. I then put the suet in and compress it until filled.
Beyond the basics of fat and cornmeal/flour, you can add raisins, craisins, molasses, millet, sunflower seeds, sunflower hearts etc. There is no magic. Just be mindful of who you are feeding. Several of my over-wintering (or year round) bird friends do not eat seeds: Bluebirds, Carolina Wren, Pine Warbler, Yellow-rumped Warbler and Hermit Thrush. Your providing calorie dense suet will help these birds survive the cold. Our winter in VA is already much colder than it was in the past few years. However, about 5 years ago, the winter was so harsh, the Bluebird population suffered (per an ornithologist lecture I attended).
Not my Bluebirds...I put out suet everyday and I had 6 Bluebirds that feasted and survived all winter.
In addition to suet, and seed, ensure that your bird friends have access to fresh water.
And..if you position your water and food where you can watch out a kitchen window, that is all the more enjoyment you will receive
