Boil a large pot of salted water.
Wash the potatoes and cut them in half.
Preheat the oven to 400 degrees.
When the water is boiling, carefully lower in the potatoes. Cook for 10 minutes. They will not be cooked through.
While the potatoes are cooking, prepare your herb butter by softening 5 tablespoons of butter in the microwave. Place the butter in a microwave safe shallow dish or small bowl and heat for about 20 seconds. You do not want to melt the butter entirely, just soften it. If you don't have a microwave, heat the butter in a small saucepan over medium heat until just soft.
Mix the herbes de Provence into the softened butter.
Arrange the chicken pieces on a sheet pan.
Brush the chicken with the herb butter mixture. You will have quite a bit of butter leftover. Set it aside when done.
When the potatoes are done, drain them into a colander. Set aside.
Cut the red onion into thin slices.
Place the red onion and cooked baby potatoes into a large bowl.
Add the remaining herb butter to the bowl with the potatoes and red onion and toss with a wooden spoon.
Pour the potatoes and red onions onto the sheet pan, spreading them among the chicken thighs.
Add the cherry tomatoes to the sheet pan. Make sure that the chicken and vegetables are spread out evenly and not overlapping.
Salt and pepper the chicken and vegetables.
Bake for 35 minutes until the potatoes are golden brown and the chicken cooked through.
Snip some fresh parsley over the meat and veggies if desired.