1Heat oven to 450°F. In oven, melt butter in 10-inch ovenproof or cast-iron skillet, about 2 minutes. Add apples, brown sugar and cinnamon; toss to coat apples. (Pan will be very hot.) Bake 2 minutes longer; stir. Bake 3 minutes longer; stir again. Reduce oven temperature to 400°F.
2In large bowl, beat Bisquick mix, granulated sugar, buttermilk, lemon juice, vanilla and eggs with whisk or fork until blended. Pour over apples.
3Bake 25 to 30 minutes or until golden brown. Sprinkle with cinnamon-sugar. Cut into wedges. Drizzle with syrup. Serve immediately.