Fill a Dutch oven halfway with water.  Cover and bring to a boil.  Once boiling, turn the heat down to medium-low and carefully lower the eggs one at a time into the hot water.  Make sure not to over crowd the pot, so they cook evenly.

Keep the lid askew and cook for 10 to 14 minutes, depending on how you like your eggs.  Remove the eggs with a large slotted spoon and place the eggs directly into an ice bath.  Set aside to cool.

While the eggs are cooling, wash and mince the celery, then pat it dry with a paper towel to get rid of extra moisture.  Measure out the salt, white pepper, onion powder, and the mayo.

Once the eggs are cool, carefully peel them.  Rinse any remaining shells off under cold running water, then use a paper towel to dry the outside.

Cut each egg lengthwise into eighths, then turn the slices and chop into smaller pieces.

Add celery, spices, and mayo and stir well to combine, then adjust seasonings to taste.  This is a good place to stop if you want to make this in advance.  Just cover it, and store in the fridge.

Slice the croissant in half lengthwise.  Spread the egg salad on the bottom half.  Scatter the watercress on top and put on the top half of the croissant.

Serve immediately.  Any leftover egg salad should be covered and refrigerated.