Line an 8x8 square pan with aluminum foil, leaving an overhang on the sides. Coat bottom and sides of pan with non-stick cooking spray. Set aside.

Place sifted powdered sugar, butter, milk, cocoa and salt in a large microwave-safe bowl. Microwave this mixture for 2 to 2½ minutes on HIGH power (100%) until butter has melted. Remove from microwave, and stir to combine.

Immediately add chopped pecans, miniature marshmallows and the vanilla extract. Stir mixture well, until all ingredients are blended together. Pour fudge mixture into the prepared 8x8 pan, and spread fudge to cover. Place fudge in refrigerator and chill for 1 hour, or until it firms up.

Once fudge has firmed up, lift it out of pan using the extended edges of foil. Cut fudge into 1 inch square pieces. Store fudge in covered airtight container in refrigerator. Enjoy!