Personally, I don't think that 700 cals in one sitting is too much. Our bodies are capable of digesting and absorbing huge quantities of calories in one sitting (as long as you do not force too much bulk into your gut at once).
It is how your tissues respond that is the issue. If you are massive, or if you have a very rapid metabolic rate (or, if for some other reason, such as disease or rapid growth) then you will use those calories for energy, growth and repair. If you are sedentary and inactive, then those calories will be shuttled to be stored as glycogen or adipose (depending on their origin and your energy level).
If you need to eat 700 cals in one sitting - then eat 700 cals in one sitting.
Also, carbs are a very easily accessable energy source - especially those calorie dense sources you stated (pasta). As they are calorie dense, they will obviously be helpful in letting you gain weight because they will give you a lot of energy at one time.
Whether that weight be fat or tissue, is, once again, dependent on your body (growth, activity, hormones, energy status, insulin sensitivity etc etc).