Toast the pecans in the oven or in a skillet. In a saucepan, bring the cream and sugar to a boil. Reduce the heat and add the chocolate, stirring constantly. Melt completely. Simmer until a candy thermometer reads 112 °C (230 °F). Remove from the heat and pour the fudge into a bowl. Add the marshmallows and pecans and stir with a wooden spoon for 10 to 15 minutes. Spread the fudge into a parchment paper lined 13 x 23-cm (5 x 9-inch) pan. Cool completely, then cut into cubes.
