Melt the butter in a saucepan over medium heat and stir in the rice. Cook the rice until it turns translucent, and begins to toast, about 3 minutes. Stir in 1/3 of the hot milk until it has been absorbed by the rice, about 5 minutes. Pour in half of the remaining milk, and stir until absorbed before stirring in the remaining milk. Stirring in the milk should take 15 to 25 minutes total, and the rice should be mostly soft with just a little firmness in the center. Add the chocolate and 2 tablespoons of sugar, and stir 5 minutes more.
Meanwhile, bring the water, 2 tablespoons of sugar, and cinnamon stick to a simmer in a saucepan over medium-high heat. Add the pears, return to a simmer, then reduce the heat to medium, and continue simmering uncovered until the pears are tender, about 10 minutes.
Spoon the risotto into serving bowls and place pears on top.