In Super (2010), I noticed the weird concept of flashbacks within flashbacks within flashbacks.
Which was the first Hollywood movie with the same concept?
As mentioned in the Wikipedia article on narrative uses of flashbacks:
An extremely convoluted story may contain flashbacks within flashbacks within flashbacks, as in Six Degrees of Separation (1993), Passage to Marseille (1944), and The Locket (1946). This technique is a hallmark of Kannada movie director Upendra whose futuristic flick Super (2010) is set in 2030 and contains multiple flashbacks ranging from 2010 to 2015 depicting a utopian India.
IMDB flaged also Enter the void (2009) with this technique. Seems that only these movies used this kind of brain teaser. As I found only these titles, i can answer your question saying that Passage to Marseille (1944) was the first movie using this technique. If you are interested you can give a look to the detailed plot here (SPOILER) looking how the flashbacks were actually mixed.