Preheat oven to 375 degrees. Cover a baking sheet with a sheet of parchment paper or silicone liner. In a large bowl, cream together sugar and butter. Beat in the egg. Mix in the peanut butter and vanilla until mixture is smooth and creamy. Stir in salt, baking soda and flour until well combined. Roll dough into 1 inch balls and then roll in sugar. Place on baking sheet and flatten with fork. Bake for 12-15 minutes. Spread Nutella onto the flat side of one cookie. Place the flat side of another cookie onto the Nutella to form a sandwich.