Preheat the oven to 225 ° C.
Cut the butter into small pieces. Add it to a salad bowl, along with the breadcrumbs and the hazelnut pieces. Mash everything with a fork until a dough forms.
Place the preparation between two sheets of baking paper. Using a rolling pin, roll out the dough until it is 4mm thick and sized to cover the beef tenderloin. Let sit in the refrigerator for 20-25 minutes.
Peel the garlic clove and cut it into 2 pieces.
Place the beef tenderloin in a rectangular dish. Make two incisions at the top of the tenderloin and insert a piece of garlic into each slit. Using a brush, brush the beef with honey mustard.
Take the preparation out of the refrigerator. Remove the first baking sheet, then turn the dough over and cover the beef tenderloin with it. Remove the second baking sheet. Wrap the fillet well.
Bake at 225 ° C for 25 minutes.
Serve with oven-roasted winter vegetables.