1. Line a 9×13-inch pan with parchment paper so that paper hangs over the edges of the pan.
2. In a large saucepan melt butter, then add sugar, maple syrup and sweetened condensed milk and stir until combined. Stir mixture constantly over medium heat and bring to a full boil. Once boiling, reduce heat to low and boil for 3 minutes, stirring constantly.
3. Remove saucepan from heat and stir in white chocolate chips until almost smooth.
4. Add in marshmallow cream and stir until smooth.
5. Fold in 1 cup chopped walnuts.
6. Pour fudge into lined pan. Gently press the remaining 1/2 cup walnuts into fudge.
7. Refrigerate about 1 hour.
8. Lift parchment paper to remove fudge from pan and cut into 24 squares and serve.