Whisk together flour, sugar, baking powder, and salt. Whisk together buttermilk, eggs, vanilla, melted butter, and oil. Whisk egg mixture into flour mixture.
Heat 1 tablespoon butter in a large nonstick skillet over medium heat. Working in batches and adding more butter as needed, pour in 1/3 cup batter per pancake. Place 2 to 3 nectarine slices on top of each pancake. Cook until small bubbles form on surfaces and undersides are golden, about 3 minutes. Flip, and cook until golden brown, about 3 minutes. Serve with butter and syrup.