Cook garlic and oil in a small saucepan over low, swirling occasionally, until garlic is golden and semi-softened, about 12 minutes. Drain garlic-infused oil into a small bowl. Transfer garlic cloves to a second small bowl. Mash cloves using a fork or spoon; stir in palm sugar, fish sauce, and black pepper. Set aside garlic chutney and reserved oil.
While garlic cooks, set a steamer rack inside a large pot filled with 1 inch of water; bring to a boil over high. Place cabbage on steamer rack; cover with lid, and cook until bright green and tender, about 5 minutes. Remove cabbage; pat dry.
Preheat a large cast-iron skillet over high for 5 minutes. Whisk together coconut milk and ¼ cup reserved garlic oil in a small bowl. Brush cut sides of each cabbage wedge with 1 tablespoon coconut milk mixture; sprinkle wedges evenly with salt. Working in 2 batches, cook cabbage wedges in skillet until charred, 2 minutes per side.
To serve, spread 1 ½ teaspoons reserved garlic chutney over charred sides of each cabbage wedge; drizzle each wedge with 2 tablespoons chili crisp.
