It’s called Japanese Giant Red Mustard. At least that’s what the seed packet said all those years ago when I actually bought it. From then on it has self-seeded every year since. I do save seeds as well, and sprinkle them about just to be sure.
I like to use it on sandwiches, it tastes like dijon mustard in lettuce-leaf form.
I also like to use it in egg rolls. The easiest way to prep greens such as this mustard for egg rolls is to first have a large kettle of water at a simmer. Then be sure to wash the greens well, damp dry on a large towel, then lay the leaves flat on a cutting board, slicing into half-inch ribbons. Next, carefully put the greens into the water, stir, and remove from heat. Let blanch for one minute, them remove from the water and into a bowl using tongs or whatever, just so you don’t get scalded. Pour any water from the bowl. I like to thicken with just a bit of cornstarch or tapioca starch, season with lots of ginger root, black pepper, a few pinches of sugar, and a few glugs of soy sauce. Roll up into the egg roll skins according to package instructions, and deep fry to perfection. Honey mustard or wasabi paste is a great condiment.
These are one of my favorite spring/summer treats.
You might also notice a small dark red plant next to the mustard, it called Red Orach, sometimes called Mountain Spinach; if you look very closely, you’ll see it is an exact replica of the wild Lamb’s Quarters. It too comes up year after year, and I save it’s seeds also.