In a mixing bowl, combine all-purpose flour, baking soda, and buttermilk to form a soft dough. Knead gently for a few minutes until smooth, then shape it into a round loaf. Place it on a baking sheet and score the top with an 'X.' Bake in a preheated oven at 425°F for about 30-35 minutes until golden and sounds hollow when tapped. Allow to cool slightly before slicing.

Grate the potatoes into a bowl, then thoroughly squeeze out excess moisture. Heat vegetable oil in a skillet over medium-high heat until shimmering. Add the grated potato, pressing it evenly into the pan. Cook for 5-7 minutes until the edges are golden brown and crispy, then flip and cook for an additional 5-7 minutes. Set aside to drain on paper towels.

In the same skillet, add thinly sliced corned beef and fry over medium heat until heated through, about 3-4 minutes. Remove from heat and keep warm.

Using the same skillet, lower the heat and add a little more oil if necessary. Crack the eggs gently and cook sunny-side up for about 3-4 minutes until the whites are firm and yolks are still runny.

In a heatproof bowl, whisk together egg yolks and lemon juice. Place the bowl over a pot of simmering water and whisk while slowly adding melted butter until the sauce is thick and creamy, about 5-7 minutes. Season with salt and pepper.

Assemble by slicing the soda bread as the foundation. Layer on the crispy hash browns, followed by the corned beef, sunny-side-up egg, and drizzle generously with Hollandaise sauce.