According to the Mayo Clinic, hazelnuts are somewhat more fatty than almonds, per ounce by weight (the range is for whether they are roasted or not):
- Almonds - 14 - 15 g
- Hazelnuts - 17 - 17.7 g
As might be expected, hazelnuts are slightly lower in starch. These is unlikely to make any practical difference in the recipe, as both are fairly close.
You should be able to use them close to interchangeably in recipes, although their flavors will be deliciously different, of course.
As for peeling hazelnuts, there are many methods. One of the more effective techniques, which will work if you are going to toast them lightly afterwards is to blanch them in a baking soda solution. See, for example, this article from My Baking Addiction with a video of Alice Medrich and Julia Child embedded demonstrating the technique.
Yes, your pan was too hot.
Because your pan was empty when you heated it, it had minimal heat capacity, and could only lose heat by convection and radiation. Thus, it heated up quickly, and likely reached a much higher temperature than it normally could with food in it.
When you heat a pan with food in it, some of the heat is transferred to the food, and much of that heat is, in turn, lost when water in the food evaporates. This slows down the heating rate, and significantly reduces the peak temperature reached.
(Evaporating water is an extremely efficient method of heat transfer, especially at high temperatures, and even solid foods like meat and vegetables still contain quite a bit of water. Any time you put something on a hot pan and it steams or sizzles, that's the sign of water evaporating.)
Also, because you didn't have any oil or water or food on the pan, you had no easy way to gauge its temperature by eye. Normally, if you heat a pan with oil already in it, you can tell when it's hot enough just by looking at how the oil behaves. If you miss all the subtler signs, like the oil turning more runny and starting to form convection patterns, the point where it starts to change color and smoke is an unmistakable sign that you've definitely heated it too far.
With a dry pan, it's quite hard to tell just how hot it is. One trick I sometimes use is to sprinkle a few drops of water onto the pan and seeing how quickly it evaporates. (Don't do this if the pan already has oil in it!) When the drops evaporate all but instantly (but still briefly wet the surface, rather than exploding on contact or hovering over it), it's time to add the oil / butter.
Of course, the modern high-tech alternative would be to get an IR thermometer. I actually do have one, but I rarely use it — it's just quicker and easier to dip my fingers in some water and sprinkle it on the pan than to get the thermometer out of the cupboard.
Best Answer
Yes, it certainly matters. Baking is not about what goes in, it is about the structure in which it goes in (and as a consequence, the structure in which it comes out). If you start using oil instead of margarine, the results will be anything between "different" and " a disaster". Flour soaked in liquid oil behaves very differently than flour in contact with margarine, and until the time the margarine melts, a lot of other interactions should have happened, which will prevent the flour (or the other ingredients) to behave as if they had been in contact with liquid oil from the beginning.
Simply "different" is something you will get in some forgiving batters such as muffin batter (when made by the mix-everything-at-once method, also aptly named "muffin method") and some types of cookie, which will show difference in spread behavior and variables such as chewiness. Yeast doughs, which usually use the fat simply as a form of enrichment, will likely be the least affected, in fact many of them may direct you to melt a solid fat for easy mixing.
You can expect a very bad result in any short or flaky dough (pie crusts and many types of cookie), in recipes which rely on creaming the margarine (many cakes and cupcakes for the batter, and all sorts of buttercream), and laminated doughs. Probably also others, these are the ones that come first to my mind.