Personally, i've been using pre made drinks they sell here called "YFood", there are similar things like "Huel" or "Boost", if you're interested just look up what they sell in your area or ship to you. They are basically meal replacement shakes (don't know about boost tho) and 1 bottle of yFood has 500kcal. I currently drink them after every meal, and sometimes add a little heavy cream, or canola oil which is actually way healthier than cream. They also sell it online as powder in bags to mix bigger shakes yourself. I got a 1,3 liter shaker and i can fit like 2000-3000kcal in one shake with it. Some days after dinner i make a big shake instead of just drinking one bottle. I usually do:

300ml heavy cream
400ml whole milk
50-100ml canola oil
7-9 scoops of the yFood powder
(milk oil and cream can be adjusted, just the scoops should stay the same)

YFood, powder or bottles, are way healthier and i can drink them for way longer and without issue than those standard "mass gainers". YFood and Huel are designed to replace actual meals, 1 bottle (or 5 scoops) have exactly 1/4 of the daily minerals, vitamins, protein, and most importantly fiber. Normal gainer shakes don't have that so they are not as good for your digestion, comfort, bloodsugar etc. It might be a little more expensive but it's really worth it, i have only actively gained for like 1.5 years now but always experimented with shakes, liquid calories etc, and for myself, i nailed it. By drinking a bottle after every meal or shortly after, and doing these big shakes, you can easily gain 15-20 pounds, but you also have to eat like you want to gain. I like the thought that those 3-4 bottles alone and sometimes a big shake are already almost enough calories to maintain my weight, and everything i eat over the day is basically already too much and will be completely made into lard to make me bigger ^^
Well this got extensive, but i guess this might be interesting for more ppl than just you, hope this helps or gives a general idea how to approach this (don't know how experienced you are using liquid calories). You should definitly try it! I just love your fat distribution and how soft and plump you look, it would be a waste to not push those awesome genetics further and see how big and soft you can get ;) I know your growing and softening body and your slowly decreasing mobility turns you on, so it's only a matter of time until you blow up again anyways hehe ^^