Mascarpone-based creams become irreversibly grainy when overwhipped or when ingredients are not properly chilled. Keep mascarpone cold until ready to use; warm mascarpone breaks down when whipped. Cream must also be cold. Beat only until stiff peaks just form, then stop immediately. Unlike butter-based frostings, mascarpone cannot be rescued once grainy; you must start fresh. For stability in layer cakes, ensure the mascarpone cream is well-chilled before assembly and chill the assembled cake before serving. The cream should be thick enough to hold its shape between layers without squishing out when the cake is sliced.