Begin by preheating your oven to 350°F, then lining a large, rimmed baking sheet with parchment paper or spray with nonstick spray.
Whisk together the taco seasoning in a medium bowl. The whisk is optional, but makes things very easy for you!
Add the sour cream to the taco seasoning and blend well.
Place your shredded chicken into a large bowl. Use about half of the seasoned sour cream mixture to combine with the chicken. At this point, you’ll want to taste it for flavor and add more salt or pepper (or any other spice) if necessary.
Heat your non-stick skillet over medium heat. Add butter to the bottom of the skillet and, as it melts, cover the whole bottom of the pan. Toss one tortilla onto the hot skillet and toast a single side (just one side!) for about a minute or until it’s golden brown. Remove the toasted tortilla from the skillet and place onto the baking sheet, toasted side down.
Carefully wipe out the skillet to remove any butter that's too brown (or burnt), then add another slice of butter, repeating the steps to toast one side of another tortilla. While that’s toasting, add a bit of the seasoned chicken meat and cheese to one half of the non-toasted side of the first tortilla. (If you love cilantro, now’s the time to add that in, too.)
Fold the tortilla over with a spatula and press down to close it. Repeat the above steps until all your tortillas are toasted, filled, and arranged on the baking sheet. Place them in the oven for about 8-10 minutes or until the cheese is melted.
Finally, remove the quesadillas from the oven and use a pizza cutter or other tool to slice them. Serve immediately with your favorite Mexican-style garnishes, like pico de gallo, and serve some of the seasoned sour cream on the side.