May Cookout Side: Just 4 ingredients. I make it when I want dinner handled hours ahead.

This four-ingredient oven side is my answer to May cookouts when I want dinner handled hours ahead and the oven doing all the work. Think of it as a Midwestern-style baked mushroom casserole with a bubbling, umami-rich, glossy top—thanks to a simple mix of mayonnaise and soy sauce that turns golden and a little toasty at the edges. It’s loosely inspired by Japanese-style mayo glazes and old-school potluck bakes, but pared down so you can assemble it in minutes, stash it in the fridge, then slide it into the oven right before guests arrive.

Serve this creamy, savory mushroom bake alongside grilled steaks, burgers, brats, or chicken at a cookout; it’s especially good spooned over charred meats or piled onto toasted bread. For a lighter plate, pair it with a crisp green salad dressed with a sharp vinaigrette or simple sliced tomatoes with salt and olive oil to cut through the richness. It also plays nicely with roasted asparagus, grilled corn, or a pot of buttered egg noodles to soak up the glossy sauce.

Servings: 6

2 pounds cremini or button mushrooms, cleaned and sliced

Lightly grease a medium ceramic baking dish (about 2-quart capacity). This helps keep the edges from sticking and encourages that glistening, golden border as it bakes.

Spread the sliced mushrooms evenly in the baking dish, packing them down slightly with your hands or the back of a spoon. They will shrink as they cook, so a full dish is expected.

In a medium bowl, whisk together the mayonnaise and soy sauce until completely smooth and glossy. Taste a tiny bit; it should be pleasantly salty and deeply savory. If your soy sauce is very strong, you can add a spoonful more mayo to balance.

Pour the mayonnaise–soy mixture over the mushrooms, using a spatula to gently coax it into an even layer that fully covers the surface. You want a continuous blanket so it can bubble and brown evenly.

Sprinkle the shredded Parmesan evenly over the top. Try not to leave bare spots; the cheese will melt into the mayo layer and help create that umami-rich, bubbling, golden crust.

At this point, you can cover the dish tightly with foil or plastic wrap and refrigerate for up to 8 hours. This is ideal for May cookouts or busy evenings: the prep is done, and the mushrooms will start to absorb some of the seasoning while they rest.

When you’re ready to bake, preheat the oven to 375°F (190°C). If the dish has been refrigerated, uncover it and let it sit at room temperature while the oven heats, about 15–20 minutes, to prevent thermal shock to the ceramic.

Place the uncovered baking dish on the middle rack and bake for 30–40 minutes, until the mushrooms have released their juices, the sauce is visibly bubbling all over, and the top is glossy with deep golden-brown edges.

For an extra bronzed top, move the dish to the upper third of the oven for the last 5 minutes, or briefly broil on high, watching closely so the cheese doesn’t burn. You’re looking for a shimmering, slightly blistered surface with caramelized spots around the rim.

Remove the dish from the oven and let it stand for at least 5–10 minutes. The bubbling will subside, the sauce will thicken slightly, and the flavors will settle, making it easier to serve clean scoops while still steamy and luscious.

Serve hot, spooned straight from the ceramic dish, making sure each portion gets some of the deeply flavored juices from the bottom along with that glossy, umami-rich top layer.

You can swap the mushrooms for other sturdy vegetables that release some moisture but hold their shape, such as thick-cut zucchini, halved Brussels sprouts, or cauliflower florets; just keep the total volume similar so the mayo layer still forms a continuous blanket. For a smokier profile at a cookout, use smoked soy sauce or add a teaspoon of Worcestershire sauce to the mayo mixture (this keeps you within the spirit of four core ingredients while nudging the flavor). If you prefer a sharper bite, substitute part of the Parmesan with grated aged cheddar or Gruyère, which will brown deeply and add nutty notes. To introduce a gentle heat, stir a pinch of crushed red pepper flakes or a teaspoon of prepared horseradish into the mayo–soy mixture. For a lighter version, you can use a good-quality light mayonnaise, though the top may brown a bit less; avoid fat-free mayo, which can separate under high heat. Food-safety notes: Keep the dish refrigerated if you assemble it ahead, and bake it within 8 hours of assembly. Do not leave the unbaked, mayo-topped casserole at room temperature for extended periods. Once baked, treat it like any perishable dish at a cookout—limit time at room temperature to about 2 hours (or 1 hour if it’s very hot outside), then refrigerate leftovers promptly in shallow containers. Reheat leftovers in a 350°F (175°C) oven until hot and bubbling rather than microwaving, which preserves the glossy, lightly crisped top.