This is called Assisi work. It’s not 100% traditional, but the basic idea is that you stitch the VOID, rather than the object itself. It usually involves animals and is stitched with two strands at a time. One color is used for filling and a darker version of it, or black, is used for outlining.
Assisi work is that it is not traditionally done in regular cross stitch. Individual X’s are, but a row is usually made of long arm cross stitch. Look closely and see that the stitches go across two squares. I drew a crappy white line for you to illustrate…
So, to do your very own Assisi-ish Embroidery, start by selecting a pattern. I like to use filet crochet patterns. Mine is here. But they have a bunch of others here. Most aren’t near as complicated as the one I chose, so don’t stress about that. Also, there are patterns specifically made for Assisi here, a bunch of great designs in all sizes here, and some big honking medieval designs here.
Once you have your pattern, fill the void around the object with one color, using a long arm or other filling stitch. Then, outline that bad-boy in a darker color.