This sourdough havarti grilled cheese is filled with strips of roasted poblano peppers and caramelized onions for an ultra satisfying vegetarian grilled cheese sandwich. Easy comfort food perfect for lunch or dinner!

Two halves of a havarti grilled cheese stacked on top of one another with potato chips on a plate.

This havarti grilled cheese sandwich was inevitable given my quest to use caramelized onions in ev-ery-thing lately. They're probably one of the easiest "fancy" ingredients to work into a wide variety of savory meals. The mellower onion flavor and creamy texture are to die for...even if you're just eating them solo on a spoon.

Not that I know anything about that!!

Slices of bread, slices of cheese, roasted poblano pepper strips, and a jar of caramelized onions on a wooden cutting board.

Since a batch of caramelized onions coincided with having a leftover roasted poblano pepper in my fridge, making a grilled cheese with them both was a no-brainer. Peppers and onion? What a perfect combo.

If you already have long-standing grilled cheese preferences, go right ahead and add these two ingredients into your fave grilled cheese and enjoy. But if you're open to a simple but specific grilled cheese combination, keep on reading.

An open face sandwich on a plate before cooking.

Bread for a grilled cheese

While I'd probably eat cheese melted between two slabs of wood, sourdough bread is something special to use in grilled cheese sandwiches. It's well structured without many holes, so it holds up to flipping and doesn't allow all that melty cheese goodness to leak out.

Plus the tanginess adds a great flavor!

My kitchen fantasy is to have my own sourdough starter and bake loaves from there, but since I have a hard enough time keeping low-maintenance plants alive, I haven't worked up the courage to maintain something alive in my kitchen. Update 2020: I tried the whole sourdough starter thing (along with everyone else in this time) and confirmed what I already thought: it's not for me. To the bakery I will (continue to) go!

If you're buying a loaf of sourdough from the grocery store bakery section like I do, look for a wide loaf so you'll have a fair amount of surface area for cheese and toppings. Leftover chunks would be faaaabulous in a sausage strata with asiago and asparagus.

A grilled cheese sandwich sliced in half with the melted cheese pulling between the halves.

Cheese in a Grilled Cheese

Just about any kind of cheese that can melt would work here, so go to town and make this your own! I find havarti is a mild flavored cheese that melts beautifully and gets very creamy in a pressed or otherwise hot sandwich.

It doesn't get in the way of stronger flavors like the roasted poblanos, and is the perfect complement to the roasty-tangy-jammy-ness in this grilled cheese.

If you're looking for a spicier option, try pepper jack. It makes a buffalo chicken grilled cheese. Smoked gouda is another cheese I can't get enough of.

A close-up of two stacked halves of a grilled cheese sandwich showing the melty peppers and onion filling.

Recipe Notes

Both the roasted poblano peppers and the caramelized onions can be made several days ahead of time and stored in the fridge.
If you'd rather, load up your sandwich and make an air fryer grilled cheese instead of on the stovetop.
Next time I make this sourdough grilled cheese I plan to split it and serve each half with a bowl of Italian sausage soup. Kind of like a homemade Panera You-Pick-Two, for two.