Preheat oven to 350. Line a 15 x 10 x 1" baking pan with parchment paper; set aside. Trim a very thin slice from the round side of each peach half so the halves will stand flat on the baking pan. Dip peach halves in melted butter to coat. Arrange peach halves, cut sides up, in prepared pan. Sprinkle cut sides of peaches with cinnamon-sugar; set aside.
In a medium mixing bowl beat cream cheese with a mixer on medium speed until smooth. Add sugar, egg yolk & vanilla. Beat until combined. Spoon cream cheese mixture into peach centers.
Bake, uncovered, about 30 minutes or until lightly browned & softened. Serve warm or at room temperature.
NOTE: Use a purchased cinnamon-sugar mixture or combine 3 tablespoons granulated sugar with 1 teaspoon ground cinnamon.