Preheat the oven to 450℉. Line a rimmed baking sheet with parchment paper; grease it with a drizzle of olive oil.
In a large pot, cover the baby potatoes with 2 inches of cool water. Add 1 teaspoon of salt and the baking soda. Bring to a boil over high heat, then reduce heat to medium-low. Boil potatoes until fork-tender, about 15-17 minutes from boiling point.
While the potatoes boil, toast the dulse in the preheating oven - just 3-4 minutes. Then cool. Crumble with your hands or grind in a mortar and pestle.
In a small bowl, combine 1 Tablespoon powdered dulse, Old Bay, pepper and remaining half-teaspoon of salt.
Drain potatoes, then tumble them onto the baking sheet. Place another sheet of parchment paper on top. Use the bottom of the pot to crush the potatoes down to 3/4 inch thick. They will split open! Remove the top sheet of parchment and save for another use.
Using a pastry brush, generously coat each potato with 3 Tablespoons olive oil. The more time you take to brush into the crevices, the crispier the potatoes will be. Sprinkle the dulse/Old Bay seasoning over the potatoes.
Place the pan on the bottom shelf of the oven. Roast potatoes for about 20-25 minutes or until very crispy. Ovens may vary. Keep an eye on them.
While the potatoes are roasting, stir together the sour cream, pickle juice, green onions or chives and pepper. Set aside.
Remove the roast potatoes from the oven and brush lightly with remaining olive oil. Sprinkle with Montreal bagel spice. Pile your crispy smashed potatoes high on a platter and serve immediately with sour cream chive sauce.
Notes
To make dust with New Brunswick dulse (seaweed), simply toast the dulse for 5 minutes in a skillet or oven until it is crisp. Cool, then grind in a morter and pestle or crush with a knife on a cutting board. Additional toppings for smashed potatoes include but are not limited to: kimchi, crumbled bacon, chimichuri, fresh herbs, horseradish creme fraiche, Green Goddess, saurkraut...the list goes on.