Peel the squash, cut in half half lengthwise, scroop out seeds and cut each half crosswise with slices 1/4 inch thick.
In a Dutch oven melt 1 Tbsp of the butter with the oil over medium heat adding the onion and sauteeing until it begins to brown, appx 7 min.
Add the squash, the stock, the rosemary sprig to the pot and simmer until squash is tender, appx 20 min.
Preheat the oven to 400, melt the remaining 1 Tbsp of butter and stir in 2 tsp of the brown sugar. Peel the pears, cut in half lengthwise, core and cut each half into 1/4 inch slices. Then toss the pears in the butter, sugar mixture.
Put the pear slices on a baking sheet and sprinkle with the finely chopped rosemary and gently roast, turning halfway, appx 7 minutes. Chop half the pear slices and set aside.
Remove the rosemary sprig from the cooled butternut squash and puree in a blender or food processor.
When blended add the last 2 tsp of brown sugar, the half & half, salt and pepper to taste and heat soup through.
Put some chopped pear into each serving bowl of soup and lay some pear slices on top to serve.