1. Preheat your oven to 190°C (375°F).

2. In a large mixing bowl, combine the flour, cold cubed butter, and ice-cold water. Gently mix until the dough comes together. Wrap the dough in plastic wrap and refrigerate for 30 minutes.

3. Roll out the chilled dough to a thickness of about 3 mm (1/8 inch). Transfer the dough to a 23 cm (9 inch) tart pan with a removable bottom. Trim the edges and press the dough into the corners. Prick the dough with a fork and line it with parchment paper. Fill with pie weights or dried beans.

4. Bake the crust for 20 minutes. Remove the parchment paper and weights, then bake for an additional 5 to 7 minutes, or until the crust is lightly golden.

5. In a separate bowl, mix the crème fraîche, chopped dill, and a pinch of salt and pepper.

6. Arrange the smoked salmon, shrimp, sliced eggs, and cucumber on the baked pastry crust. Spoon the crème fraîche mixture over the seafood, leaving a 2.5 cm (1 inch) border around the edges.

7. Bake the tart for an additional 10 to 12 minutes, or until the filling is lightly set and the crust is golden brown.

8. Allow the tart to cool slightly before serving. Garnish with lemon wedges and fresh dill sprigs, if desired.

9. Handle hot surfaces and sharp knives carefully to avoid accidents or injuries.