This jaw-dropping, over-the-top delicious dessert, is one of the best Korean pear recipes ever! It's lovely for the holidays or a dinner party!
Preheat the oven to 400°F, adjust a rack to just above the center of the oven, and use 1 teaspoon of the butter to grease an approximately 8 x 8 x 3-inch baking dish. Set aside.
In a small saucepan, combine the water, sugar, grapefruit juice, rosemary and vanilla. Bring to a boil and then turn off the heat. Stir to ensure all of the sugar has dissolved. Set aside.
Peel the pears and then cut them in half, lengthwise. Use a melon baller to remove the seeds from each half, and then a paring knife to cut out any remaining stem.
With a very sharp paring knife, cut as many slits as you can, and as thinly as you can, horizontally, into the round side of the pear halves. Do not cut all the way through the pear! Your knife should stop about about 1-inch from the bottom.
Place the pears in the preheated 400°F oven and set the timer for 15 minutes. Use a small ladle or a soup spoon, to baste the pears, again getting the syrup into the slits. (The slits will become more open as they roast, and it will therefore become easier to do this.) Continue to set the timer and baste every 15 minutes, until you've reached 1-1/2 hours. Then add about 1/4 teaspoon of the remaining teaspoon of butter, to the top of each pear. Place them back in the oven for a few more minutes. If they are not golden on top, place them under the broiler for about 30 seconds. (Watch them carefully in the broiler!)
Pour all of the syrup from the baking dish back into the saucepan, and bring to a boil. Then turn the heat to low and simmer until it's reduced by about half, and has thickened. Now strain the syrup into a small bowl or serving pitcher.