Place a nonstick skillet or cast-iron skillet on the stovetop over medium-low heat. Allow it time to preheat with no oil or anything in it.
Generously spread 1 ½ tablespoons softened butter on all four sides of two slices of bread. Add ½ tablespoon butter to the skillet and allow it time to melt and become foamy.
Place 2 slices of buttered bread into the skillet, evenly top each slice of bread with the ⅓ cup mozzarella cheese and ⅓ cup havarti cheese in the pan, and the 2 slices of buttery bread on top.
You can also completely build the sandwich outside of the skillet instead. Allow it to cook for 2 to 3 minutes.
Use a spatula to flip the sandwich to the other/opposite side, press it down, and allow it to cook for an additional 2 to 3 minutes.
Carefully remove your grilled cheese sandwiches from the skillet. Serve immediately and pair it with a warm bowl of soup, salad, pickles, or salty potato chips. Enjoy!
Notes
Select the right skillet! Use a heavy bottom skillet or griddle pan. I prefer to use a cast iron skillet.
Cook on medium low heat, medium heat will even be too high. You don't want to cook your sandwich at too high heat or your bread will be toasty, but your cheese won't melt. A little patience is key, trust me it still won't take long.
Be generous with the butter. Slather enough butter on the bread to cover it and add a little to the pan as well. Try to allow your butter time to come to room temperature so that it spreads easily.
Press the sandwich down, this is why it's important not to use thinly sliced bread. Flip it once.