In a medium bowl, stir together flour and salt.

Using your fingertips, work in butter until mixture resembles coarse meal.

Drizzle in 5 tablespoons ice-cold water and stir with a fork until a dough forms.

Gently knead together and shape into a disk. Cover with plastic wrap and refrigerate for at least 2 hours or overnight.

Meanwhile, preheat the oven to 350°F.

Prick sweet potatoes all over with a fork and place on a parchment paper-lined baking sheet. Roast until just barely tender, about 30 minutes.

When potatoes are cool enough to handle, peel off and discard skin. Thinly slice potatoes and set aside.

Line a baking sheet with parchment paper. On a lightly floured surface, roll out dough into a 14-inch circle.

Gently spread cheese over dough, leaving a 2-inch border around the edge.

Arrange potatoes on dough, overlapping as necessary but maintaining the border, and scatter salmon around and between potatoes.

Fold pastry border over filling, pleating as you go, to form a rustic galette.

Carefully transfer to the prepared baking sheet and brush crust all over with some of the cream. Drizzle remaining cream over filling.

Bake until crust is golden and potatoes are tender, about 50 minutes.

Slice and serve warm, with chives scattered over the top.