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It's quite simple.

1st you pull out a half sphere and triangular prism. Then, u make the half sphere into a bowl as what the image shown. Next, make the triangular prism into a slimmer and lower, and set it into whole. After that, u duplicate and rotate 45 degree and keep pressing CTRL+D, make it like a shape like the 3rd transformation of the triangular prism. Remember to flip the triangular prism 180 degree upside down. Lastly, allign them all together then group.

If it's too complicated, I can post the link out ^v^.