For a richer flavor, marinate the chicken in the spice paste for at least 30 minutes, or even overnight, before cooking. Adjust the amount of cayenne pepper and bird's eye chiles to suit your desired level of spiciness. Remember that the flavor will intensify as the vindaloo simmers. If you don't have bird's eye chiles, you can substitute with serrano peppers or another hot chili pepper of your choice. Serve over basmati rice or with naan bread for a complete and satisfying meal. A dollop of plain yogurt or raita can help to cool down the spice.