If you google for "italian hand calligraphy" the first few specimens you see are basically it. I believe they used a straight holder and possibly a stub nib to yield those teardrop terminals. What this person on instagram is doing is essentially the same thing, except they've gone with a spencerian style of weighting rather than italic. I don't have any resources on how you can learn this but the basic idea is to have an even black, i.e if you sort of blur your letters it should look even throughout the text, use PS or sort of squint your eyes to do this. Like say after it's blurred if you see areas where it's slightly thicker in black those are your problem areas, if it's too white, those have spacing issues, so on and so forth. I dunno where instagram woman got her idea from but a man who exaggerated it quite a bit about 10-20 yrs ago was tony di spigna, however he did it using lettering but the process to how he did it is exactly how you'd do for something like the instagram example you linked.