I was under the impression that cooking ketamine referred to the practice of turning pharmaceutical ketamine vials into the powder via evaporating the solvent. If you have pure ketamine HCL, just mix it with water, preferably bacteriostatic/saline.
Step by step what I have done in the past is to put a desired amount of powder in a cup, boil some tap water (risky, if you use bacteriostatic you don't have to boil anything) and draw 1,1ml of it in a needless syringe. Then I would drop the liquid from the syringe into the cup with the powder and stir it until there's no visible particles, then stir it a bit more. It dissolved very nicely especially since my water was heated a bit. Now I draw this solution through a filter into the syringe and voila, ready to inject.
Make sure it's 100% ketamine before you IM though. Really wouldn't recommend IM'ing anything but sterile vials.