Core and cut the nectarine into slices. Cook in a pot over low heat until softened.
Beat the mascarpone in a bowl with a hand mixer until fluffy. Put amaretti cookies in a resealable freezer bag and bash to pieces with a rolling pin. The cookies pieces should still be chunky, with very little fine powder.
Put a few nectarine slices in the bottom of a trifle glass. Add a layer of mascarpone. Sprinkle with some amaretti pieces. Layer until the top of the glass is reached, then garnish with remaining nectarine slices and a finishing sprinkle of amaretti. Enjoy!