Oooh! I can help you out!
There is a lady in my area, very nice lady and is trying very hard to get her business going, and she makes AMAZING horse cookies.
I first met her at a Dressage Show where Nelson and I won Champion for Training Level 1,2,3,4 tests - and we won a container of her cookies.
Oh my goodness gracious, Nelson has NEVER wanted cookies like he does these. He hunts them down if he can smell them, he will literally stick his face in my pockets and my Fanny Pack *yes I wear one when I hunt of hack, I have asthma and I have to carry my inhaler and Epi Pen* until he gets one.
Here is her website, I swear by these cookies! Everyone in the area buys them and they are even being sold at all the tack stores here. The Horse Cookie > Home
If you take your index finger and thumb and make a circle out of that - that is the size of these cookies. Perfectly round, dark brown, smell absolutely amazing *even I want to eat them* they are an inch thick.
These cookies are very popular here.
Look into them if you can!