In a small saucepan, bring the cream to a boil. Pour over the chocolate and let melt for 1 minute. With a whisk, stir until the sauce is thick and smooth. Set aside.
With the rack in the middle position, preheat the oven to 425°F (220°C). Generously butter a 12-cavity doughnut pan.
In a bowl, combine the sugar and cinnamon.
In another bowl, combine the flour, baking powder, baking soda, nutmeg and salt.
In a third bowl, cream the butter, oil and brown sugar with an electric mixer. Add the egg and beat until smooth. At low speed or using a wooden spoon, stir in the flour mixture alternately with the yogurt until smooth.
Spoon the batter into a pastry bag fitted with a plain tip. Pipe the batter into each cavity of the pan.
Bake for 7 minutes or until a toothpick inserted into the centre of a doughnut comes out clean. Unmould onto a parchment paper-lined wire rack. While still hot, coat with the cinnamon mixture. Return to the rack and let cool.
Serve with the warm chocolate sauce.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.