Celebrated Pittsburgh chef Derek Stevens of Union Standard spreads a mayonnaise on burger buns that’ll have you drooling til the cows come home. It’s not just any mayonnaise, you see: it’s marrownaise, a silky, fatty, meaty substance that transforms regular beef into a rich umami experience. We spoke with him to learn more about this wonderfully savory concoction and see if we might even be able to recreate it at home. Spoiler alert: there’s no real recipe — you’ll just need mayo-making supplies and a few big marrow bones.

What is the origin story of this wonderful-sounding condiment?
I love bone marrow and I’ve used it in all different ways, so I thought it would be an interesting accompaniment. It’s a basic mayonnaise with lemon juice, vinegar, mustard, oil, rendered bone marrow and egg yolks. We serve marrownaise with our french fries, too. The reason I wanted to serve it with fries was that the taste reminds me of McDonald’s fries [before the chain switched to vegetable oil]. A good friend has a restaurant in Pittburgh where he does beef tallow fries. It’s odd how much I remember that taste.

Do you use marrownaise on anything else on the menu?
We also use marrownaise as a condiment to season our steak tartare, which gives it a unique flavor for a steak tartare. The mayo has that specific “warm roasted meat umami,” which we mix with cold raw meat, so you get an extra deep beefy flavor. I think it would be great on a turkey sandwich, too. Or you could pair with fried cauliflower, add a nice meaty flavor to some veggies.

Can we make it at home? Is there a trick or two we should know?
Sure! It’s a little in-depth and there’s a lot to it, but you can totally do it. We roast pipe-cut marrow bones and drain off all the rendered marrow. Then we make a mayonnaise. Put a little warm tap water in while you’re mixing it up, because what’s really important is that the marrow is room temperature. You don’t want it hot or cold. Too hot and the mayo will break, too cold and it will solidify. It’s a ratio of about 75% blended oil and 25% marrow. Even with 25% marrow, it still carries so much of that flavor. Then you can save the bones and still make stock.

What’s something to keep in mind when making mayonnaise in general?
If you have the opportunity to make mayo instead of buying it, it’s a whole different world. You want to have good-quality farm eggs and a healthy dose of Dijon mustard (an emulsifier) and you can experiment with vinegars and citrus. Start very slowly, then speed it up, paying attention to the consistency. As it gets really thick, if you add a drop too much oil, it’ll break. If it starts to get too thick, taste it — if it’s not quite right, add water or lemon juice.

How long has the burger with marrownaise been on the menu?
The whole time we’ve been open! I wanted to do a pretty simple straightforward high- quality burger, not a bunch of ridiculous bells and whistles on it. It’s indicative of the rest of our menu in that we do food that’s good and simple. We use a local grass-fed beef from Jubilee Hilltop that has a great fat content. We add a local white cheddar, and we don’t make the buns yet but we have a local bakery that makes them just for us. It’s a potato roll with everything bagel spice on top that gives it a little extra crunch and flavor. We cook it on a really high heat griddle or a cast-iron skillet instead of the grill. You have to get that nice sear and crust on it.