Place ricotta, berries, lemon zest, vanilla and icing sugar in a food processor and blitz briefly until just combined. Alternatively, simply mix all ingredients together well in a mixing bowl.
Crush biscuits to a rough crumb in a food processor. Alternatively roughly break up biscuits, place inside a clean dry plastic bag, cover with a tea towel and crush with a rolling pin or heavy wine bottle.
To assemble parfaits, divide crushed biscuits between 4 dessert glasses (leave 2-3 tablespoons crushed biscuits for garnish). Pour over 1 tablespoon berry liqueur. Top with ricotta mixture, dividing equally. Finally, top with berries and garnish with extra crushed biscuits.