Bring a large pot of heavily salted water to a rolling boil. Add the trimmed green beans and cook for exactly 3 minutes until they are bright green but still crisp.

While the beans cook, prepare a large bowl filled with cold water and ice cubes.

Immediately drain the green beans and plunge them into the ice water bath to stop the cooking process. Once cooled, drain thoroughly and pat completely dry with a clean kitchen towel.

Heat the extra-virgin olive oil and 2 tablespoons of the unsalted butter in a large skillet over medium-high heat.

Add the sliced mushrooms to the skillet in a single, even layer. Cook undisturbed for 3 to 4 minutes until the bottoms develop a rich, golden-brown crust. Flip and sauté for an additional 2 minutes.

Reduce the skillet heat to medium. Add the finely minced garlic to the center of the pan and sauté for 60 seconds, stirring constantly until intensely fragrant, ensuring it does not burn.

Toss the blanched and dried green beans into the skillet with the mushrooms and garlic. Season with sea salt and freshly ground black pepper.

Sauté and stir continuously for 2 to 3 minutes until the green beans are thoroughly heated through and coated in the garlic butter.

Remove the skillet from heat. Add the remaining 1 tablespoon of butter, allowing it to melt over the hot vegetables. Drizzle with fresh lemon juice if using, and toss with the chopped fresh parsley before serving.