Place trivet in pressure cooker and add 1 cup water.
Slice lemons thinly and remove all seeds.
Sprinkle all sides of the chicken with bitters and sprinkle with black pepper (optional). Place on trivet in pressure cooker
Cover the chicken with lemon slices (and stuff in the cavity for whole chicken).
Seal the lid and cook at high pressure:whole chicken, 8 minutes a poundbone in chicken pieces, 12 minutesboneless chicken pieces, 6-8 minutes
Keep pressure cooker closed for 8 minutes after cooking, then release the remaining pressure.
Place chicken (in a single layer for pieces) on a broiler pan with some of the lemon slices. Broil on high until the chicken is browned, about 5 minutes.