Melt butter over medium heat in a large wok; pour in olive oil. Add chile peppers, garlic, peppercorns, cardamom pods, cinnamon, turmeric, and cumin. Add chicken; stir-fry in the mixture until fully covered and starting to brown, about 5 minutes. Add potato, pepper, and onion; continue to stir-fry for 5 minutes more.

Stir coconut milk into the chicken mixture. Reduce heat to low and let simmer, stirring occasionally, until sauce has thickened, about 30 minutes. Remove from heat; stir in yogurt.