• Preheat oven to 375F.  
• Melt the butter, and combine with the olive oil.  Spread about 1/3 of the butter/oil mixture on the bottom of a 11x9 inch (or similar size) baking pan. Season the bottom of the pan well with salt and pepper. 
• Wash and scrub the sweet potatoes thoroughly. Use a mandoline to slice the potatoes into thin, even slices slices.

   
• Arrange the sweet potato slices in the baking pan. Do this by grabbing a bunch of the slices at the same time so they stick to each other and you can just place them in the baking pan standing up. Insert slices of red onion in between every 2-3 potato slices. You don't have to be exact, just start sticking them in there.

   

   
  
• Brush the tops of the potatoes with the rest of the butter/oil mixture, and season well with salt and pepper. 
• Cover with foil and bake at 375 for 35-45 minutes, or until the potatoes are almost fully cooked.  
• Remove the foil and turn the heat up to 450F. Bake for another 10 minutes, or until the tops of the  potatoes are fully cooked and the potatoes get nice and crispy.

   
• Top with the salsa verde.

   

Parsley Salsa Verde

• In a small food processor or personal blender, combine the parsley, garlic, lemon zest, lemon juice, capers, and ~4 tablespoons of olive oil. Process until all the parsley is finely chopped. Add more olive oil as needed until you reach the desired consistency. I ended up using 10 tablespoons of olive oil.

   
• Season with salt and pepper to taste - start with a dash or two and add more if needed.