In a small saucepan, melt the unsalted butter over low heat. Once melted, add the saffron threads and let them steep for about 10 minutes. Remove from heat and set aside.

Season both sides of the sirloin steaks generously with salt and pepper. Heat a skillet over medium-high heat and add the saffron-infused butter once hot.

When the butter is bubbling, add the steaks. Cook for about 4-5 minutes on each side for medium-rare, or adjust according to your preferred doneness. Remove the steaks from the skillet and let them rest for a few minutes before slicing.

In the same skillet, add the olive oil and smashed garlic cloves. Sauté over medium heat for 2-3 minutes until fragrant and lightly golden. Be careful not to burn the garlic.

Add the fresh spinach to the skillet and toss until wilted, about 2 minutes. Drizzle with lemon juice and sprinkle with red pepper flakes if using. Toss to combine and then remove from heat.

Slice the rested sirloin steaks and arrange them on a plate. Spoon any remaining saffron-infused butter over the steak slices. Serve the sautéed spinach alongside the steak. Enjoy!