Add fish sauce, fresh lime juice, minced garlic, and sliced chili. Taste and adjust balance — it should be salty, sour and slightly sweet. Set aside to cool to room temperature.

Crab Salad

Drain any excess liquid from the crab meat and transfer to a medium mixing bowl. Gently break up large lumps so the crab stays flakey.

Add minced shallot, chopped cilantro, sliced scallion, and diced cucumber to the crab.

Pour 1/2 cup of the prepared nuoc cham over the crab mixture, add 1 tbsp lime juice and 1 tsp neutral oil, then season with 1/2 tsp sea salt and 1/4 tsp black pepper. Gently fold to combine, taking care not to overwork the crab. Taste and add more nuoc cham or salt if needed.

Cover and refrigerate the crab salad for at least 20 minutes (up to 1 hour) to let flavors marry. Keep chilled until assembly.

Red Curry Crema

In a small bowl, whisk together mayonnaise and sour cream until smooth.

Add Thai red curry paste, lime juice, honey and salt. Whisk until evenly combined. Adjust seasoning — add a little more lime for brightness or a pinch more curry paste for heat. Chill until ready to assemble.

Assembly & Finish

If tostadas are not fully crisp, warm them briefly in a 350°F (175°C) oven for 3–5 minutes to refresh their crunch; cool slightly.

Spread about 1 teaspoon of red curry crema on each blue corn tostada, creating a thin base layer.

Divide the chilled crab salad evenly among the 6 tostadas (about 2 oz crab salad per tostada), mounding gently in the center.

Drizzle about 2/3 teaspoon of sweet chili sauce over each crab mound. For extra brightness, spoon a scant 1 teaspoon of reserved nuoc cham around the crab (not so much that it softens the tostada).

Garnish each tostada with a couple of radish slices, a few micro cilantro leaves, and a light sprinkle of toasted sesame seeds if using.

Serve immediately with lime wedges on the side for squeezing.