Place butter and vanilla extract in small bowl. Scrape seeds from one vanilla bean piece. Whisk to blend. (Can be made up to 1 week ahead. Cover and refrigerate.).
Place eggs and next 4 ingredients in large bowl. Scrape in seeds from remaining vanilla bean piece. Whisk batter to blend.
Place bread slices on work surface; spread with apple butter. Reserve 1/4 of peach slices for garnish. Arrange remaining peach slices over 6 bread slices. Top with remaining bread slices, apple butter side down.
Melt 2 tablespoons vanilla butter in heavy large skillet. Transfer 3 sandwiches to skillet. Cook until brown and cooked through, about 5 minutes per slide. Transfer to plates. Repeat with remaining 3 sandwiches.
Spread thin layer of remaining vanilla butter over each sandwich; cut in half diagonally. Drizzle with warm maple syrup. Scatter reserved peach slices over; sprinkle with powdered sugar and top with whipped cream if desired.