How can I default embedded posts to “square” formatting?

With the default WordPress embed feature, you can paste your own link into your post and it embeds a snippet of the post, with an image. I’m having trouble where — at times — a rectangular image is used, which alters the layout.

Is there anyway to just make all of these embeds use the “square” formatting and layout?

IE:

• First line: Title.
• Second line: Image with the excerpt to the right of the image.

Example: Here’s the layout I get when an image qualifies as “rectangular.”

However, I’d prefer all instances to simply appear as follows.

How can I accomplish this?

Thank you!