I have done it its easy,
Zucchini (baby marrow)
Broccoli
Potato skins
Peas
Spinach
Carrots
Crayfish/sardine/pilchard (optional, but the fish love it)
Multi vitamin
Gelatin
1. Place all food stuff in pot just covered with water, bring to boil and then let simmer for about an hour till every thing is soft
2. Add multi vitamin
3. Put all ingredients through a blender, the finer the better
4. If mixture is too watery leave on a low heat to reduce liquid.
5. When mixture is nice and thick add gelatin and mix well.
6. Take a flat backing try line with silicon paper.
7. Spread mixture onto silicon paper evenly and thinly
8. Dry mixture out in a very low heat oven
9. When dry peal from silicon paper and crunch it up in your hands
NB. If you do not have silicon paper, you can use the backing try, once dry you will need to scrape off with a spatula
NB. When drying mixture out in oven it must not cook, only dry out. This process takes some time so be patient.
NB. Quantities I play with all the time, the cooked mixture is usually about 1 liter, and I use 2 multi vitamins and 1 20g packet of gelatin.