6 ounces semisweet chocolate, finely chopped
2 ounces unsweetened chocolate, finely chopped
2 tablespoons unsalted butter, cut into 1/2-inch cubes
1 1/2 cups granulated sugar
1/2 cup plus 2 tablespoons heavy cream
3/4 cup Marshmallow Cr?e
2 teaspoons vanilla extract
25 toasted pecan halves

Position oven rack in center of oven and preheat to 350 degrees F. Spread the pecans in a single layer on a baking sheet and lightly roast for 5 to 8 minutes, or until fragrant. Transfer the nuts to another baking sheet and cool completely.

Line an 8-inch square baking pan with aluminum foil, leaving a 2-inch overhang on two opposite sides. Lightly butter the bottom of the foil-lined pan.

Place the chocolates in a large heatproof bowl.

Butter sides of a heavy, non-corrosive 2-quart saucepan. Add sugar and cream. Stirring constantly with a wooden spoon, cook the mixture over medium-low heat for 10 to 15 minutes, or until the sugar crystals are completely dissolved. Using a pastry brush dipped in warm water, dissolve any crystals clinging to the side of the pan. Bring the syrup to a full boil without stirring. Bubbles should appear all over the entire surface of the syrup. Boil the syrup without stirring for 5 minutes. Pour the hot syrup over the chocolates and butter. Let stand 30 seconds to melt the chocolate.

Using a rubber spatula, stir until smooth. Stir in the Marshmallow Cr?e and vanilla extract. Scrape the fudge into the prepared pan. Arrange pecan halves over the top of the fudge. Refrigerate 60 minutes or until set.

Lift the fudge out of the pan using the two foil ends as handles. Invert the fudge onto a cutting board and carefully peel the foil off the fudge. Invert again onto a smooth cutting surface. Using a large knife, score the fudge into 25 pieces. Cut the fudge, rinsing the knife with hot water and wiping dry in between each cut. Store fudge in an airtight container at room temperature.