IT'S TIME to be thinking about Christmas... time to be making the Christmas pudding, the mincemeat and the Christmas cake. If you haven't enough dried fruit to make all three, make up the amounts with chopped dates and home-made candied peel. Christmas Pudding (for 4) Ingredients: 2 oz. plain flour, 1/2 level tea- spoon baking powder, 1/4 level teaspoon salt, 1/2 level teaspoon grated nutmeg, 1/4 level tea- spoon cinnamon, 1 level teaspoon mixed spice, 3 oz. sugar, 1/2-1 lb. mixed dried fruit, 4 oz.