Step 1: Whisk together rice flour, cornstarch, coconut milk, water, and turmeric in a bowl until smooth, then let rest for 15 minutes—this hydrates the flour for better texture.
Step 2: Heat a 10-inch non-stick skillet over medium-high heat (375°F) and add 1/2 tablespoon of vegetable oil.
Step 3: Sauté pork belly slices for 3–4 minutes until lightly browned, then push to one side of the skillet.
Step 4: Add onion slices and cook for 1 minute until slightly softened.
Step 5: Stir the batter briefly and pour about 1/2 cup into the skillet, immediately swirling to coat the bottom thinly.
Step 6: Scatter bean sprouts over half of the pancake and cover the skillet with a lid for 2 minutes to steam the sprouts.
Step 7: Uncover and cook for another 3–4 minutes until the edges curl and turn golden brown and crispy.
Step 8: Fold the pancake in half over the bean sprouts using a spatula, then transfer to a plate.
Step 9: Repeat steps 2–8 with remaining batter and ingredients, adding oil as needed to prevent sticking.
Step 10: Serve immediately with fish sauce for dipping.