Pierce the potatoes several
times so moisture can escape during baking. Place in the oven and bake until fork-tender,
45 minutes to 1 hour.
When just cool enough to handle, peel the potatoes and press through a ricer
into a large bowl. Add salt, baking powder and egg white. Add the flour a little
at a time and mix with your hands until a rough dough forms; do not overwork.
Put a large pot of salted water on to boil.
Transfer the dough to a lightly floured surface, and gently knead until smooth,
1 to 2 minutes, adding a bit more flour if needed to prevent sticking. Divide into
4 portions and roll each into a rope about 1/2-inch thick. Cut rope into 1/2-inch
lengths. Gently roll each piece down the back of a cheese grater or fork to create
slight ridges, or press it to form a small dimple. (The indentations help hold the
Gently place the gnocchi, a few at a time, into the boiling water, removing them
with a slotted spoon a minute or two after they rise to the surface. Drain well
and transfer to a warm platter. (Or refrigerate or freeze for future use.)
To make the sauce: Melt the butter in a saucepan over medium heat, and sauté
the garlic until soft, about 2 minutes.
Add the cream and chicken broth; cook until
reduced by almost half. Stir in the sage, lemon zest and cheese. Pour over the gnocchi,
toss gently and serve immediately.