Cut the zucchini and yellow squash into 1/2-inch thick half-moons, keeping them roughly uniform in size so they cook evenly. Mince the garlic and have all ingredients measured and ready before you start cooking—this ensures you can focus on proper searing without interruption.

Heat the butter and olive oil in a large skillet over medium heat until the butter is foaming and the oil shimmers. Add the zucchini and yellow squash in a single layer, then sprinkle with sea salt and black pepper. Resist the urge to stir—let them sit undisturbed for 2-3 minutes to develop a golden, caramelized crust on one side. I find this initial searing creates a much better texture than stirring constantly from the start.

Stir the vegetables and add the minced garlic and red pepper flakes, cooking for another 5-7 minutes until the squash is tender and the garlic is fragrant. The vegetables should be soft but still hold their shape. I like to add the garlic after the initial sear so it doesn't burn and develops a sweeter, more delicate flavor.

Remove from heat and top with freshly grated Parmesan cheese if desired. Serve immediately while the vegetables are still warm and the cheese melts slightly into the dish.