Mike Taulty [0] has been posting ~2 posts per month on creating applications for the HoloLens (he just published his 13th yesterday) - he's a UK Microsoft Developer. There are a few other smaller blogs that occasionally post stuff like Abhijit's Blog (inactive) [1] and El Bruno [2]. Althought not a blog, the HoloLens subreddit sometimes has some interesting posts, but a lot of the time it's just articles about AR or videos of people showing off a demo (and not code or explanations per se) [3]. Lastly I recommend looking at the WindowsAppDev Daily Digest, as sometimes stuff is posted there regarding the HoloLens, or tangentially related topics [4].

[0] https://mtaulty.com/?s=Hitchhiking

[1] https://abhijitjana.net/category/hololens/

[2] https://elbruno.com/category/hololens/

[3] https://www.reddit.com/r/HoloLens/

[4] http://windowsappdev.com/