There is less of a difference than you might think. Heck, with the addition of a little calcium chloride (to help bind the milk particles), you can even make cheese with skim milk. I flipped through Harold McGee's section on low-fat milk, and he doesn't give any warnings about using it in cooking.
Of course, keep in mind that your result won't have quite the same texture. I doubt you'll notice unless the milk is the primary ingredient in the sauce (and there's no other thickening agent) or primary liquid in the dough. If I was forced to come up with a way to adjust to using low-fat, I'd probably add a little more milk if I was going for flavor, or a little less if I was going for texture.
Abstract: Ganache is delicious, but not everyone eats dairy. We examined whether coconut milk can be used for the creation of a non-dairy ganache. We ran a series of experiments. The answer is that, with some creative techniques, you can use it, but it does not come anywhere near to the real thing.
Introduction. Someone wrote a question on Seasoned advice about coconut based ganache and we got curious.
Background. We love ganache even more than pure chocolate, and make it often ourselves, so we think we have all the prerequisites needed to create and judge a coconut based ganache recipe. Our favorite ganache recipe 1 (which we used as a starting point) is: 100 g chocolate, 72% cocoa (only made from cocoa, sugar, and cocoa butter, no vegetable fat or emulsifiers); 100 g cream, at least 30% (non-UHT), 25 g butter.
Method. We prepared the base mix as follows: 25 g coconut milk were heated until boiling. They were removed from the heat. 25 g chocolate (72%) and 6g cocoa butter were added. Everything was left to dissolve. After 5 minutes, the mixture was whipped with a handheld mixer at the second-to-highest setting. This was Version 0. It was divided in two batches. Different versions were made from each batch by gradually adding guar (a knife-point-ful), egg yolk (1, in lieu of lecithine) and sugar (8g per batch). Each version was whipped for at least 3 minutes. The final versions (1c and 2b) where put for 30 min in the refrigerator, then taken out and whipped again. As there were no observable changes after the cold whipping, we do not treat them as a different version. We also made a small portion of dairy ganache for comparison purposes.
Results. These are listed in Table 1. The numbers in the ingredients columns of the table represent the order of adding the ingredients to the mixtures.
Table 1. Experiment results.
The final consistency of version 1c is documented in Figure 1. Note that the peaks do not drip and you can rotate the bowl at 180° without anything falling out. The piece of chocolate was added for color comparison.
Figure 2 shows a zoom of the blue bordered area in Figure 1.
Discussion. It is possible to make a profiterole filling with coconut milk based ganache, but it isn't quite like the real deal. Also, it resembles non-whipped ganache more closely than whipped ganache.
The basic ganache recipe can be done with coconut milk instead of cream and cocoa butter instead of butter. However, it tastes fattier than real ganache, and it is runnier. Unlike dairy ganache, whipping does not result in aeration.
We think that eliminating the cocoa butter altogether will somewhat alleviate the fatiness problem, but we did not test this proposal yet.
A thickening and or emulsifying agent can improve the ganache texture. Even though egg yolk improves aeration, is not a good choice, as it results in a slimy feel. Guar is a better solution.
The addition of sugar ruins the chocolateness of the taste. If bitterness is not desired, a sweeter chocolate (50%) should be used. Only dedicated sugar lovers or Americans should resort to adding sugar. In that case, it should be added before the guar (we would suggest dissolving it in the coconut milk before boiling it) as not to interfere with the texture of the final product.
Threats to validity. First, there was a single tester (the quasi-royal we). Second, this tester is already biased in favor of dairy products in general and specifically for dairy based ganache. Third, many interesting combinations (including xanthan gum and corn starch) could not be tested due to lack of resources.
Conclusion and outlook. We found the experiment very inspirating. It was also yummy. But we'd like to issue an warning: This experiment is dangerous. In the preparation phase, we discovered a penchant for guared coconut water deep fried in coconut fat we'd rather not have known about. Nevertheless, we are looking forward to offering the results for peer preview to a chocolate-loving lactose intolerant co worker.
References: 1 My own recipe book
Best Answer
No, you can't substitute any of those for paneer. This should be pretty obvious given that you're trying to skewer and grill the paneer. It's a firm cheese that doesn't melt, while any combination of milk, yogurt, cream cheese, and butter will melt, if it's not liquid already. The best substitutes would be other cheeses like halloumi that don't melt, or else tofu. A firm cottage cheese would probably also do okay.
You also can't really use a cheese that melts in something like this. First of all, it just could never be the same texture, and the flavor would be a bit different too. But it could be worse than that. You didn't say exactly how much pumpkin, onion, and breadcrumbs you have in there, but generally, if you put a melting cheese in there, it's at best going to make the whole thing less solid and at worst it'll drip out as you grill it or conceivably even let it fall apart.
But you can indeed make paneer with the low fat milk, though. The texture just won't be quite as good - a little tougher, more dry and maybe even crumbly - since there's less fat and relatively more protein. With whole milk, 2L of milk makes ~350 grams of paneer, though that can of course vary depending on how well you drain/press it. Low fat milk won't have quite as high a yield, but you can probably still just start with 2L. The texture is probably the bigger problem. (And it'll of course be worse if your milk is 1% than if it's 2%.)