Preheat oven to 425°F.
Slice tomatoes in half, lengthwise, and remove seeds.
Lay out on baking sheet, skin side down.
Scatter the garlic cloves between the tomatoes.
Drizzle some olive oil over the tomatoes and garlic cloves. Make sure the cloves are well coated with the olive oil (you may need to pick up the cloves and rub them with the olive oil).
Sprinkle the thyme over the tomatoes and garlic, followed by a bit of kosher salt. Next coat the tomatoes and garlic with a few grinds of black pepper.
Roast the tomatoes for 45 minutes. The thickness of the tomatoes will really determine the roasting time. If they are thinner, the roasting time may be less, if they are thicker, the roasting time may be longer. The longer they roast, the more concentrated the tomato flavor.
Once everything is roasted, remove from the oven and pour into the 2 quart saucier.
Add the chicken stock to the pan and bring to a simmer over medium high heat.
Once stock is bubbling, remove from heat and pour into a blender and pureé. (remember to vent the lid!).