Preheat the oven to 350 degrees F. Place 2 Tbsp. of the butter and brown sugar in a small pot and set over medium heat. Cook, stirring occasionally, until the sugar melts. Mix in the flour until well combined. Very slowly whisk in the cream. Bring the mixture to a simmer and simmer 1 to 2 minutes, until lightly thickened. Remove from heat and stir in vanilla. Brush the bottom of a 9" x 13" baking pan with the remaining butter. Place the apples, lemon juice and cinnamon in a bowl and toss to coat. Arrange the apples in the baking pan, cut side up. Spoon the caramel sauce over the apples, sprinkle with the pecans, cover with foil and bake about 40 minutes, or until the apples are just tender. Set two halves in each of 4 serving dishes, spoon the sauce overtop and garnish with a mint sprig. If desired, top with a dollop of whipped cream or a scoop of vanilla ice cream.