In a small saucepan, melt the unsalted butter over medium heat. Add the fresh sage leaves and cook until the butter turns golden brown and the sage is crispy, about 5-7 minutes. Remove from heat and let it cool slightly.

Stir in the lemon juice and salt into the brown butter. Pour the mixture into a bowl and refrigerate until firm.

In a large skillet, heat 2 tablespoons of butter and 1 tablespoon of olive oil over medium heat. Add the peeled cipollini onions and a pinch of salt. Cook, stirring occasionally, until the onions are golden brown and caramelized, about 15-20 minutes.

Add the balsamic vinegar to the skillet and cook for an additional 2 minutes. Remove from heat and set aside.

Preheat the oven to 400°F (200°C). Season the filet mignon steaks with salt and black pepper.

In a large oven-safe skillet, heat 2 tablespoons of olive oil over medium-high heat. Sear the steaks for 2-3 minutes on each side until browned.

Remove the skillet from heat and sprinkle the chopped thyme and breadcrumbs evenly over the steaks, pressing gently to adhere.

Transfer the skillet to the preheated oven and roast for 8-10 minutes for medium-rare, or until desired doneness.

To serve, arrange the caramelized cipollini onions on each plate. Place the filet mignon on top and add a dollop of the brown butter & sage compound butter. Garnish with additional thyme if desired.