To make the dressing whisk together the mayonnaise, milk, sugar, vinegar and poppyseeds. Refrigerate until ready to serve.
To roast the pears: Peel, cut in half and core the pears. Put a teaspoon of butter into each hallowed out part of the pears, sprinkle with thyme and drizzle with honey. I added pieces of bay leaves on top. Bake in 400° oven for one hour. When cool enough to handle cut into thin slices or cubes.
For salad: In large bowl add the romaine and arugula, raspberries, pears, pistachios and blue cheese. Toss lightly. Add the poppyseed dressing and carefully toss to coat all the ingredients. Serve immediately.
Note: Dried cranberries would be a great substitute for the raspberries and you can use the pears fresh without roasting.