1. Pat the cooked king crab meat dry with paper towels, then gently chop or tear it into bite-size pieces, removing any bits of shell as you go.

2. In a medium mixing bowl, whisk together the mayonnaise, crème fraîche or sour cream, Dijon mustard, lemon zest, lemon juice, minced shallot, kosher salt, and black pepper until smooth and well combined.

3. Add the chopped king crab meat, chopped chives, and chopped dill to the bowl, then gently fold everything together with a spatula until the crab is evenly coated but not smashed. Adjust seasoning with more salt, pepper, or lemon juice to taste, and add the Old Bay seasoning or paprika if using.

4. Cover the bowl and refrigerate the crab mixture for 20–30 minutes to allow the flavors to meld and the dressing to slightly thicken, which makes it easier to spoon onto the bases.

5. While the crab mixture chills, prepare the cucumber bases by slicing the cucumber into thin, even rounds and patting them dry with paper towels so they stay crisp. Arrange the slices on a serving platter.

6. For baguette bases, slice the baguette into 1/2-inch rounds, brush each slice lightly with melted butter, and place them on a baking sheet. Toast in a 375°F (190°C) oven for 5–7 minutes, or until lightly golden and crisp at the edges, then let cool to room temperature.

7. To assemble, place a small leaf of baby arugula or a pinch of microgreens on each cucumber round or toasted baguette slice, then top with a heaping teaspoon of the chilled crab mixture, forming a neat mound on each base.

8. If using salmon or trout roe, spoon a tiny amount on top of each crab mound, then sprinkle with a bit more chopped chives or dill and a light grind of black pepper for color and freshness.

9. Arrange lemon wedges around the platter and serve the appetizers slightly chilled, allowing guests to squeeze a little lemon juice over their bites just before eating.