Grilled Cheese with Asiago, Gruyere and Soft Onions

There is a difference between the grilled cheese you make for a kid at noon and the one you make for adults at a party, and most of it comes down to the cheese. This version uses two: Asiago, which is nutty and a little sharp, and Gruyere, which melts into long, sweet strings. Between them go onions cooked slowly in butter until they are soft and starting to brown, and thin slices of roasted tomato. The bread is buttered on the outside and toasted until it shatters. Made one at a time it is a fine supper. Made twenty at a time and cut into triangles, it is the hot hors d'oeuvre that empties first.

The two cheeses

Gruyere does most of the melting. It has enough moisture and fat to flow, and its flavor gets sweeter and deeper when warm. Aged Asiago is drier and firmer; on its own it would sweat oil and stay a little stiff, but paired with Gruyere it adds a salty, sharp edge that keeps the sandwich from tasting flat. I use them in equal weights and put one cheese against each slice of bread, so both get direct heat and both melt.

Slice the cheese thin, or shred it on the large holes of a box grater. Thick slabs melt from the outside in, and by the time the center goes soft the bread is past golden. Shredded cheese melts fastest of all, which matters when you are cooking in batches.

If you can't find aged Asiago, a good aged white cheddar takes its place nicely and gives the sandwich a slightly more New England accent.

Onions and tomato, both done ahead

The onions should be soft and sweet, not raw and crunchy. Cook chopped onion in butter over medium heat for 10 to 15 minutes, stirring now and then, until it is limp and the edges have gone light brown. Season with a pinch of salt. For a party I cook a whole skillet of them the day before and refrigerate them.

Raw tomato makes a grilled cheese soggy. Roasting it first concentrates the flavor and drives off water. Slice plum tomatoes into thin rounds, lay them on a parchment-lined sheet pan, brush with olive oil, season with salt and pepper and roast at 400°F (200°C) for about 20 minutes, until they look a little shriveled at the edges. These also keep for a day in the refrigerator.

The bread

Choose a sandwich loaf or a sourdough with a tight crumb, sliced about 1/2 inch thick. Open, holey bread lets the cheese leak through onto the pan. A loaf with a little seed or spice in it is fun here: a sesame loaf, or a rye with caraway, gives the sandwich more character without stealing the show.

Butter the outsides, edge to edge. Soft butter spreads without tearing the bread; if yours is cold, mash it with a fork first. Some cooks spread mayonnaise on the outside instead, which browns very evenly. Either works.

From the recipe box

Grilled cheese with Asiago, Gruyere, onions and roasted tomato

4 sandwiches, or 32 party triangles

Prep

15 min

Cook

40 min

Total

55 min

Show amounts in

US cups & spoons metric

Fillings

• 1 medium (about 8 oz)1 medium (about 225 g) yellow onion, finely chopped
• 1 tbsp15 g butter, for the onions
• 44 plum tomatoes, sliced into 1/4-inch rounds
• 1 tbsp15 ml olive oil
• 4 oz115 g aged Asiago, thinly sliced or shredded
• 4 oz115 g Gruyere, thinly sliced or shredded

Sandwiches

• 8 slices8 slices sandwich bread or tight-crumbed sourdough
• 4 tbsp57 g butter, softened, for the bread

Method

1. Heat the oven to 400°F (200°C). Lay the tomato slices on a parchment-lined sheet pan, brush with olive oil, season and roast for 20 minutes, until shriveled at the edges.
2. Meanwhile melt 1 tbsp butter in a skillet over medium heat, add the onion and a pinch of salt and cook 10 to 15 minutes, until soft and lightly browned.
3. Butter one side of each bread slice and lay them buttered side down on the counter.
4. Cover four slices with Asiago and the other four with Gruyere, then divide the onions and tomatoes over the Asiago slices.
5. Close the sandwiches, pairing an Asiago slice with a Gruyere slice so the buttered sides face out.
6. Heat a heavy skillet or griddle over medium-low heat and cook the sandwiches 3 to 4 minutes, covered, until the underside is deep golden.
7. Flip, press lightly with a spatula and cook 3 minutes more, uncovered, until the second side is golden and the cheese is running at the edges.
8. Rest 1 minute on a board, then cut into halves for supper or into eight small triangles for a party.

Notes from the kitchen

• A lid over the skillet traps heat so the cheese melts before the bread scorches.

Low and covered beats hot and fast

The usual mistake is too much heat. On high, the bread browns in 90 seconds and the cheese is still cold. Medium-low and a lid give you a deep golden crust and a fully melted middle at the same moment. When you flip the sandwich, leave the lid off so the first side doesn't steam soft.

Making many at once

Nobody wants to stand at the stove flipping sandwiches while the party happens in the next room. There are two good ways to scale up.

On a griddle: an electric griddle or a large stovetop griddle across two burners holds six to eight sandwiches. Set it to about 325°F (165°C), cover the sandwiches loosely with a sheet pan turned upside down to trap heat, and work in rounds.

In the oven: this is my choice for a crowd. Heat the oven to 450°F (230°C) with a rimmed sheet pan inside for 10 minutes. Lay the assembled sandwiches on the hot pan, buttered side down, put a second sheet pan on top, and bake for 6 minutes. Lift off the top pan, flip the sandwiches and bake 4 to 6 minutes more, until both sides are golden. Two half sheet pans hold 12 sandwiches, which is close to 100 triangles.

Party quantities and timing

Cut each sandwich into quarters on the diagonal, then cut each quarter in half again for small triangles that people can eat in two bites. Count on three or four triangles per guest when there are other hors d'oeuvres.

The day before, cook the onions and roast the tomatoes. The morning of the party, assemble the sandwiches, stack them between sheets of parchment, wrap the stack and refrigerate. Bake straight from the refrigerator, adding a minute or two. Cut them on a board with a long serrated knife and pass them within 10 minutes. If they need to wait, hold them in a 200°F (95°C) oven for up to 20 minutes, uncovered so they stay crisp.

Serving

A small bowl of grainy mustard or a spoon of tomato jam alongside is welcome. As a main, serve a whole sandwich with a bowl of soup or with a sharp salad, such as greens with pears, Asiago and cashews, which echoes the cheese. At a cocktail party, they balance a cold platter like the salmon mousse. You will find more small bites under Party Food and Hors d'Oeuvres. The last tray always disappears faster than the first.