Preheat an oven, then line a rimmed baking sheet with parchment paper. Place the salmon fillet on top, then drizzle with neutral oil, Kosher salt, granulated garlic, 1 tsp lemon zest, and black pepper. Bake. Remove and allow to cool.
Roll out the puff pastry to ¼” thickness, or roughly 12”x14”, doesn’t have to be exact. Use a knife or pizza cutter to slice into squares. Coat a standard muffin tin well with nonstick cooking spray, then place each square of pastry into the tin. Bake. Remove.
Whisk together eggs and heavy cream with Kosher salt.
Divide the chopped watercress, cooked salmon, potatoes, dill, and thinly sliced scallions between each muffin mold. Pour the egg and cream mixture on top.
Transfer to the preheated oven and bake until the puff pastry is golden brown and the filling has puffed up. Serve with additional dill, if wanted, and a little sour cream.