Split the English muffins and toast them until golden. Spread 1 tablespoon unsalted butter across the cut sides while still warm (reserve remaining butter for spinach).

Sauté spinach

In a medium skillet over medium heat, melt the remaining 1 tablespoon butter. Add the baby spinach and sauté until just wilted, 1–2 minutes. Season with 1/4 tsp kosher salt, 1/4 tsp black pepper and a squeeze (about 1/4 lemon) of lemon juice. Keep warm.

Poach Eggs

Fill a wide, shallow saucepan with 3–4 inches (about 8–10 cm) of water. Bring to a gentle simmer (not a rolling boil). Stir in 2 tablespoons white vinegar. Reduce heat so the surface is gently moving with small bubbles.

Crack each egg into a small bowl or ramekin. Using a spoon, create a gentle whirlpool in the simmering water and slip one egg at a time into the center (or submerge 2 at once if pan allows). Poach eggs for 3–3.5 minutes for runny yolks or 4–4.5 minutes for slightly firmer yolks.

Using a slotted spoon, lift eggs from water, draining briefly, and place on a paper towel-lined plate. If needed, trim any ragged whites with kitchen scissors. Keep warm in a warm (not hot) place or return to gently warm water off the heat for up to 5 minutes before serving.

Make Caper Hollandaise

Set up a double boiler: simmer a saucepan of water and place a heatproof bowl over it (bowl bottom should not touch water). Off the heat, whisk 3 egg yolks with 1 tablespoon fresh lemon juice and 1/2 tsp Dijon mustard until slightly thickened.

Place the bowl over the simmering water and whisk constantly. Very slowly drizzle in the 6 tablespoons melted warm butter (in a thin stream), whisking continuously until the sauce thickens and emulsifies. If sauce becomes too thick, whisk in 1 tsp warm water at a time to loosen. Keep the hollandaise warm over the pan (off direct heat) but do not overheat or it will split.

Remove from heat and stir in 1 tablespoon chopped capers, 1/4 tsp salt and a pinch of white pepper or cayenne. Taste and adjust lemon or salt as needed. Hold warm.

Assemble

Place the toasted, buttered English muffin halves on two plates. Divide the sautéed spinach evenly and mound on each muffin half.

Arrange 3 ounces (about half) of smoked salmon over the spinach on each muffin.

Gently place two poached eggs (one per muffin half if serving open-faced; or both on a single muffin for a two-egg stack) on top of the salmon.

Spoon generous amounts of the warm caper hollandaise over each poached egg, allowing some to run down the sides.

Garnish with the remaining extra capers and a sprinkle of chopped fresh dill. Serve immediately with an extra lemon wedge on the side.