Place a 2-quart glass trifle bowl in refrigerator to chill.

To Make the Jelly: In a 3-quart saucepan, combine sugar, lemon juice, and 1 ½ cups (350ml) water (see note) and heat over medium heat until sugar is completely dissolved. Add berries and bring to a boil. Reduce heat to maintain a simmer and cook, skimming any foam that accumulates on the surface, until berries are tender and have released their water, about 10 minutes (skimming off foam produces a clear jelly).

Meanwhile, in a small bowl, whisk together gelatin and 3 ½ tablespoons (50ml) water. Set aside to let gelatin bloom.

Strain berry mixture through a fine-mesh strainer set over a medium heatproof bowl, pressing gently on berries to extract as much poaching liquid as possible. Transfer poached berries to a medium bowl and set aside. Pour poaching liquid into a 1-quart measuring cup and add enough additional cold water to reach 2 ¼ cups (550ml). Taste and adjust with sugar if needed.

Pour ½ cup (120ml) of poaching liquid into now-empty saucepan and heat over low heat until steaming. Remove from heat and whisk in prepared gelatin mixture until homogenous and no gelatin lumps remain.

Whisk gelatin mixture into remaining poaching liquid, then transfer liquid to a medium bowl. Place bowl in an ice bath and chill, stirring occasionally, until jelly is slightly thickened and temperature reaches 60°F (16°C), 20 to 30 minutes.

To Assemble the Trifle: Remove trifle bowl from refrigerator and set on work surface. Line bottom of bowl with genoise sponge cake, top with reserved poached berries, and drizzle with sherry (if using). Pour cooled jelly on top and return bowl to refrigerator until jelly is set, about 2 hours.

Arrange fresh berries in an even layer on top of jelly (if desired, you can place the berries around the inside perimeter of the bowl in a decorative pattern, then fill the middle space with the remaining berries). Spread crème légère evenly over berries.

In the bowl of a stand mixer fitted with the whisk attachment, whisk heavy cream and sugar (if using) on medium-high speed until soft peaks form. The whipped cream should be spoonable and not stiff. (Alternatively, in a medium mixing bowl, whisk heavy cream by hand until soft peaks form).

Spoon whipped cream on top of crème légère and place trifle in refrigerator until cold, about 30 minutes. If desired, top whipped cream with additional berries, toasted almonds, or sprinkles. To serve, scoop generous portions into individual bowls and serve immediately.