Onion-Smothered Cheese-Studded Turkey Burgers

Update June 2010: in June 2009 I switched to eating gluten-free, egg-free, dairy-free and nearly vegan, so this recipe predates the switch (by almost a year). I would not eat this recipe today, but I wanted to note that with a little tweaking, it can be made gluten-free.  Substitute the flour with rice flour, and serve on gluten-free buns or english muffins. I cannot think of a way to veganize the recipe however. 

 Since Labor Day weekend is around the corner, WCW is a burger recipe this week. This recipe is my take on Rachael Ray’s Onion and Mushroom Smothered Super Swiss Turkey Burgers, which is possibly the only Rachael Ray recipe that is not on one of her sites. It’s in her 2-4-6-8 Great Meals for Couples or Crowds book on page 126, and I did find it online here.
My husband cannot eat mushrooms, so I doubled the onion and tweaked some other things. I have basically gotten this to the point where all the ingredients are things always in the freezer, fridge or pantry, which is nice. The recipe calls for Swiss Cheese, but I have successfully substituted the following cheeses instead: Monterey Jack, Gruyere, Comte, Manchego, various hard local cheeses and and even just basic cheddar.
Onion-Smothered Cheese-Studded Turkey Burgers, adapted from Rachael Ray’s 2-4-6-8 turkey burger recipe
Makes 4 burgers

4 sandwich-size sourdough english muffins, split and toasted (CGL Note: I often just use regular sized ones, or sourdough rolls, or even slices of sourdough bread. You could use buns or Kaiser rolls, but I do think the tang of sourdough is nice here.  For gluten-free, use gluten-free bread)
Directions
Preheat large skillet over medium-high heat with the 1 tablespoon of olive oil. Add onions (CGL Note; you can season with salt and pepper now, I just prefer to season at the end). Cover pan with foil and set a lid or plate on top to smother onions, for 10 minutes. Stir occasionally. Uncover pan and let juices cook off a little. Sprinkle with the flour. Cook for 1 minute; add vinegar, then chicken broth (or water) and cook sauce until nice and thick, about 5 minutes.
Combine ground turkey, cheese, poultry seasoning, and cayenne pepper in a medium bowl. Score the meat with the side of your hand to separate it into 4 equal amounts. Form the mixture into 4 large patties no more than 1″ thick. Drizzle the patties with olive oil. Preheat a large nonstick skillet over medium-high heat. Once the skillet is hot, add the patties and cook them for 5-6 minutes on each side, or until turkey is cooked through.
Serve the burgers on the toasted English muffins, smothered with the onions.