Preheat the oven to 350&
In a large bowl, combine the flour and 1 1/2 cups of the sugar, and mix well. Add the melted butter, lemon juice, lemon zest, and the 3 beaten egg yolks. Stir in the buttermilk.
Beat the 3 egg whites with the remaining 1/4 cup sugar until stiff, and gently fold into the first mixture. Pour into the loaf pan, place the pan in a water bath (a large baking dish with about an inch of hot water), and bake until brown on top and puffed above the rim of the loaf pan, for about 1 hour.
About 10 minutes before the pudding is finished baking, prepare the Blackberry Coulis.
Serve warm or at room temperature. To serve, spoon the pudding onto plates, add 2 tablespoons Blackberry Coulis around the pudding, and top with whipped cream and confectioners' sugar.
Makes 8 servings.