Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.

In a large bowl, toss the thinly sliced potatoes with salt and black pepper until evenly coated.

Drizzle half of the olive oil onto the prepared baking sheet. Arrange half of the potato slices in a circular pattern, overlapping them slightly to form a galette shape.

Drizzle the remaining olive oil over the first layer of potatoes. Top with the remaining potato slices in the same circular pattern, pressing down gently to compact the layers.

Bake the galette in the preheated oven for 45-50 minutes, or until the potatoes are golden brown and crispy. Check for doneness by inserting a fork; it should easily pierce the potatoes.

While the galette is baking, prepare the sour cream sauce by mixing the sour cream, chopped dill, and lemon juice in a small bowl. Set aside.

Once the galette is done, remove it from the oven and let it cool for about 10 minutes. Carefully transfer it to a serving platter.

Top the galette with slices of smoked salmon, capers, and red onion. Drizzle with the sour cream sauce and garnish with fresh dill sprigs before serving.