Heat a small nonstick skillet over medium heat. Add panko breadcrumbs and toast, stirring constantly, until evenly golden, about 3–4 minutes. Remove to a plate to cool.

Toast sesame seeds

In the same skillet over low heat, add the sesame seeds and toast 1–2 minutes until fragrant. Remove and set aside.

Lightly butter the brioche or split rolls. Place cut-side down on the skillet over medium heat and toast until golden and crisp, about 1–2 minutes. Keep warm.

Make the Crab Filling

Combine wet ingredients

In a medium bowl whisk together the mayonnaise, Greek yogurt, Dijon mustard, Worcestershire sauce, lemon juice and lemon zest until smooth and evenly combined.

Add aromatics

Fold in the finely minced shallot, diced celery and thinly sliced chiles (or crushed red pepper) to the mayo mixture. Stir until distributed.

Season

Add Old Bay seasoning, sea salt and black pepper. Taste and adjust: add up to 1 tsp more lemon juice or a pinch more salt if desired.

Fold in crab gently

Gently fold the fresh crab meat into the sauce mixture until evenly coated. Be careful to preserve lumps of crab; do not overmix. If using a small cooked whole crab garnish, crack and reserve some pieces for plating now.

Add crunch

Fold in the toasted panko and toasted sesame seeds. The mixture should be moist but hold together when scooped; add another tablespoon of panko if excessively wet.

Assemble & Finish

Place a small handful of microgreens or baby arugula on the bottom half of each toasted brioche. Spoon a generous portion (about 1/2 cup) of the crab mixture onto the greens, mounding slightly in the center.

Top with reserved crab pieces or soft-shell garnish if using. Finish with an extra scattering of chives and a light squeeze of lemon over each sandwich.

Set the top bun on each sandwich and serve immediately with lemon wedges on the side.