1. Heat oven to 375 degrees F.
2. In a bowl, combine pie crust mix, the 3 tablespoons brown sugar and 1/3 cup pecans. Stir in amount of water recommended on the crust box for making a double crust pie; continue stirring until dough forms.
3. On lightly floured surface, roll dough out to 13-inch circle. Transfer to large ungreased baking sheet.
4. Halve and pit plums; cut each half into 4 slices. Toss slices in bowl with remaining 1/3 cup brown sugar, remaining 1/3 cup pecans and the flour. Mound in center of pastry circle, topping with any sugar mixture left in bowl. Fold border up over filling, working around circle.
5. Bake in 375 degree F oven for 35 to 40 minutes or until the filling is hot and the crust is golden. Cool galette on baking sheet on wire rack. Serve slightly warm. Makes 12 servings.