Preheat a convection oven to 325°.
In a large bowl, stir together 1 ½ cups sugar, salt, flour, lemon juice, grated zest, buttermilk, heavy cream and 5 egg yolks until well incorporated. In a separate mixing bowl, beat the egg whites with a whisk until they hold stiff peaks. Gradually whisk in ½ cup sugar until it is completely incorporated. Fold the beaten whites into the mixture in 3 different additions, allowing the last addition to remain only partially mixed in. Don’t over mix. It should be lumpy with some of the egg whites in large visible clumps—it should look messy, soupy and lumpy—not neat and smooth!
Transfer mixture to a 10- by 12- by 3-inch (12 cup) baking dish. For the water bath, place the baking dish in a larger baking pan and pour simmering water into the outside pan until it reaches ⅔ up the side. Bake for about 60 minutes, until the top turns dark golden brown and the pudding starts to set up underneath. It will always remain slightly loose when shaken. Cool completely and refrigerate until serving.
To serve, scoop each serving onto a dessert plate and spoon huckleberry sauce along the side.
Put all of the ingredients together in a small nonreactive saucepan. Turn on the heat and bring this to a simmer for 5 minutes. Remove the saucepan from the heat, cool slightly and purée with burr mixer or in the blender. Store in the refrigerator up to 2 weeks.
This recipe makes plenty of sauce with enough for ice cream or more pudding. Divide in half if you prefer.
Recipe by Steve Johnson, The Red Dory, Tiverton