Salted Caramel Buttermilk Brown Sugar Muffins

"These easy, one-bowl, no-mixer muffins are soft, wonderfully moist, and the crumb has the perfect balance of density and lightness. The batter has melted butter, oil, and buttermilk to keep the muffins fluffy and tender. Don't overfill your muffin pan because the muffins rise very well. While baking, the butter and brown sugar caramelize, creating subtle caramel undertones. Although they don't 'need' it, I played up the caramel profile by drizzling with salted caramel. Make your own or use storebought. Use the batter as a jumping off place and try adding chocolate chips or glaze them with another favorite...."