Gaining

eat what you like just more of it.
There is no magic food that will make you gain weight faster.
Drinking heavy cream adds lots of fats so you can try that.
If you like milkshakes start having those several times a day.
Eat a bowl of ice cream before bed that has worked for me.
Gaining weight takes time and effort and you have to wait for your body to adjust to the extra food and calories. Once your metabolism slows down then you will start to gain.
Its different for everybody so if someone says X number of calories eaten in a day equals Y number of pounds gained doesn't know what they are talking about.

Can I get the high calories and fat, WITHOUT so much suger? I do not mind some, but just not overly sweet

sugar is carbs. potatoes and pasta will spike your blood sugar just like a slice of pie.

I have had success with little fat bombs, taking doses of oil (preferably non GMO, so canola is out, olive oil would be great), 25 ml or 50 ml max per dose, I chased it down with a softdrink, so I could not taste the oil. You can also use heavy cream, but has less fat per dose and animal fats at that.
In my case, the trick with the oil was, to space it in 8 hour intervals, so that the stomach can digest that much fat. In my case, it has made me fatter reliably, it is responsible for the last 30 pounds I gained. I have never done it for a week or more, that might be a lot of fat, but theoretically you could be able to gain really fast like this, the dose of pure fat makes any meal into a huge fat bomb, no matter what you ate.

I have noticed from others and my experience that if one takes pure fat or cream, they overdo it and drink too much at once and the stomach cannot digest that much fat at once.

This is of course if you (like me) are interested in fattening and gaining foremost, this is not really tasty or delicious.