Preheat oven to 375 degrees. Cut the pears in half, removing top stems and scooping out any seeds in the center. Arrange in a casserole dish with the cut sides facing up.
Make the caramel sauce
To a medium saucepan, add all of the caramel ingredients. Place over medium high heat for 20-30 minutes until reduced by 1/3.
Bake the pears
Pour the caramel sauce over the pears, cover the dish with foil and place in the oven for 30 minutes (if using the convection setting). Remove the foil and cook for another 10-15 minutes until done
Toast the walnuts
To a low-sided pan, add the walnuts, rosemary and pinch of salt. Toast on medium until fragrant, remove from the pan (discard the rosemary) and roughly chop.
Serve
Plate each serving with two slices of pear, a drizzle of the caramel sauce from inside the pan, and some of the toasted walnuts on top. Garnish with fresh rosemary if desired. Serve warm.