Heat a large soup pot over medium heat and add the olive oil.
Add the minced garlic, grated ginger, chopped lemongrass, and chopped Fresno chile; cook 1–2 minutes until fragrant and softened.
Pour in the chicken broth and add the cubed potato; simmer uncovered for about 15 minutes until the potato is fork-tender.
Add the corn, coconut milk, and sweet Thai chili sauce; cook about 5 minutes more until the corn is tender and bright.
Reduce heat to low, stir in the butter and shredded fontina cheese, and cook over low heat, stirring often, until the cheese melts and the soup is creamy.
Remove the pot from heat and stir in the chopped basil, cilantro, and a pinch of salt and pepper; keep warm while you fry the shrimp.
Set up three shallow bowls: flour mixed with salt and pepper; beaten eggs; and a mixture of panko and shredded coconut.
Working in an assembly line, coat each shrimp first in the flour, then dip in the beaten eggs, and finally dredge in the panko-coconut mixture; place on a plate.
Heat about 1–2 inches of coconut or canola oil in a heavy, high-sided skillet over medium heat. When hot but not smoking, fry shrimp in batches 2–3 minutes per side until light golden.
Transfer fried shrimp to a paper towel–lined plate to drain and repeat with remaining shrimp.
Ladle chowder into bowls, garnish with diced mango, extra basil and cilantro, a squeeze of lime if desired, and top with warm coconut fried shrimp; serve immediately.
