"astonished how" is a correct and usable phrase in written English.
You can use it when you want to express your surprise at something. For example: "I am astonished how quickly the changes happened."
"Everyone was astonished how big it was," said Selina.
In London he was "astonished how acquiescent" British society was.
We have been astonished how good most of these events are.
"I am continually astonished how casually people speak about other residents of the common European house," he said.
And I was astonished how someone had approached me and actually remembered what my essay was about.
"I was astonished how many people were out there and how many people were cheering," she said.
But the absolute numbers (6,900 Greeks and 3,900 Spaniards during those six months) are still modest.It is "astonishing how astonishing it still is that they are coming", says Holger Kolb, at the Expert Council of German Foundations on Integration and Migration.
"Let it become your second nature". After reading 12 pages of Lenin he noted in his diary: "Astonishing how that cheers me up and clears my mind.
Most Rev Justin Welby said that it is "astonishing" how much food is being wasted and left uneaten despite the number of people desperately resorting to food banks to feed themselves and their families.
Gewirtz notes that it is "astonishing how much [Arthur Conan] Doyle took from him" in Sherlock Holmes's supercilious manner and more.
"I was astonished at how magnificent these images were and how beautiful and timeless," he said.
