Turkey bolognese can be thickened by adding tomato paste to the dish right before adding your crushed tomatoes. If you don't have tomato paste, there are a few other ways to do it.  1. Sprinkle 1 tablespoon of gluten free all purpose flour in with the onions and olive oil (after the onions are cooked down). Whisk over medium-high heat until the flour starts browning slightly (2-3 minutes), then add 3/4 cup of liquid (like gluten free vegetable stock). Whisk until it starts to thicken, then add your other ingredients as directed. You can add another tablespoon olive oil if needed.  2. Whisk 1 tablespoon of corn starch with 1/4 cup of cold water (make sure there's no lumps) or vegetable stock. Add to the dish when you add the crushed tomatoes and stir well over medium heat. As the corn starch heats up, it will thicken the bolognese sauce.  3. If you follow the recipe as-is and it's only a little bit too thin, add an extra one or two tablespoons tomato paste. Or increase the cooking time by another 5-10 minutes, stirring often, to cook the sauce down.