Preheat oven to 375 degrees.
Cut, fennel bulb into 1/4 inch slices. Arrange the fennel on a baking sheet drizzle with olive oil and a pinch of salt. Bake until fork tender and golden brown, about 45 minutes.
Bring a large pot of salted water to boil.
Wearing gloves, pull the nettle leaves off the stems. Discard the stems. Prepare a large bowl filled ¾ of the way with cold water and ice. Add nettles to boiling water and cook just for a minute or two, until the nettles are bright green. Drain the nettles and add to the ice water.
Squeeze out all of the water and roughly chop. Add the nettles and olive oil to a food processor or blender and pulse until finely chopped, stopping to scrape down the sides as necessary. Add parsley, garlic, red wine vinegar, lemon juice and shallot and pulse a few more times. Season with salt and pepper to taste.
Sprinkle steak with salt. Heat a large cast-iron skillet over high heat. Add oil to pan and then steaks; cook 3 minutes on each side or until browned. Reduce heat to medium-low, add butter and crushed garlic to pan. Carefully grasp pan handle using an oven mitt. Tilt pan toward you so butter pools; cook 1 1/2 minutes, basting steaks with butter constantly. Remove steaks from pan and let stand 10 minutes, then cut into 1/2 inch slices. Serve with roasted fennel and chimichurri drizzled on top.