You'll relish this simple yet versatile condiment

Whenever I can put a little effort into something and have it pay off in spades, I'm happy. Such is the case with Red Onion-Mustard Relish.

This homemade condiment, made with caramelized red onions, balsamic vinegar and whole-grain mustard, takes less than 30 minutes to make. Whenever I have it on hand, I find myself turning to it to add flavor to dishes again and again.

It's easy to make. Simply sauté chopped onions in a little butter until they are golden brown, splash in a little vinegar and spike it with a generous amount of grainy mustard.

It can stay in your fridge for up to a week, if it lasts that long. I use it in a variety of ways to make my meals better.

This week I made it to top a juicy, roasted pork tenderloin. Its sweet-tartness was the perfect foil to the simple Dijon-coated roast, turning it into a sophisticated Sunday dinner.

Two days later, when I needed to get a dinner on the table quickly, I added it to grilled ham and cheese sandwiches. It was so good I don't think I'll ever look at a plain grilled cheese sandwich the same again.

The next night, I added a couple of spoonfuls to a basic balsamic vinaigrette that I'd warmed slightly in a large skillet before tossing it with baby spinach, thinly sliced steak, crumbled blue cheese and cherry tomatoes for a light but flavor-packed spinach salad.

When I got down to the final couple of tablespoons of the relish, I had to carefully consider how to best use it. After all, it's good stuff and I wanted to do it justice.

With that in mind, I mixed it with a couple of tablespoons of olive oil and brushed it on a large piece of naan bread, which I topped with a few slices of Brie, thinly cut prosciutto and sliced fresh figs and baked in a hot oven until it was brown and the cheese was melted. Oh, my. Justice was certainly done.

Yes, all these meals could have been made without the relish, but trust me, they wouldn't have been nearly as good. If all I have to do is caramelize some onions to have a week's worth of memorable meals, count me in.

Meredith Deeds is a cookbook author and food writer from Edina. Reach her at meredith@meredithdeeds.com. Follow her on Twitter ­at @meredithdeeds.

Serves 4.

Note: Sweet and tart, the onion-mustard relish pairs beautifully with the Dijon-coated pork tenderloin. From Meredith Deeds.

• 2 tbsp. Dijon mustard

• 1 tbsp. olive oil

• 1/2 tsp. salt

• 1/4 tsp. freshly ground black pepper

• 1 1/2 lb. pork tenderloin

• Red Onion-Mustard Relish (recipe follows)

Directions

Preheat oven to 450 degrees. Spray rimmed baking sheet with cooking spray.

In a small bowl, whisk together the mustard, olive oil, salt and pepper.

Trim silver skin or connective tissue off tenderloin with a very sharp thin knife.

Place tenderloin on baking sheet. Coat tenderloin with mustard mixture and roast for 23 to 27 minutes, or until cooked to desired doneness (at least 140 degrees).

Let meat rest for 10 minutes, transfer to a carving board, slice and serve with the Red Onion-Mustard Relish.

Makes 1 3/4 cups

Note: From Meredith Deeds.

• 2 tbsp. unsalted butter

• 2 medium red onions, chopped

• 1/2 tsp. salt

• 1/4 tsp. freshly ground black pepper

• 1/4 c. balsamic vinegar

• 1/4 c. sugar

• 3 tbsp. whole grain mustard

Directions

Heat the butter in a 12-inch nonstick skillet over medium-high heat. Add the onions, salt and pepper and cook, stirring frequently, for 5 to 7 minutes, or until the onions are beginning to brown.

Reduce the heat to medium and continue to cook, stirring occasionally, for 10 to 15 minutes, or until the onions are browned. Add the vinegar and sugar, and cook for another 5 minutes or until almost all of the liquid has been evaporated. Remove from heat and stir in the mustard.