In a medim saucepan, stir together the custard powder and 1/4 cup sugar. Slowly add milk, whisking to prevent lumps. Bring to a boil, until completely cooled, about 10 minutes. Mix in the yogurt and vanilla.
Transfer the custard to a heatproof bowl and set it in a large bowl of ice, stirring occasionally, until completely cooled, about 10 minutes. Mix in the yogurt and vanilla.
To assemble the trifle: Spread 1/2 cup of the custard on the bottom of a 3L-4L glass bowl. Stand some of the strawberries in a ring against the sides of the bowl. Add half of the cake cubes.
Drizzle with 1 tablespoons liqueur, if using, over the cake. Add half the berries and half the remaining custard. Repeat layers.
Recipe can be made ahead up to this point. Cover and chill in the refrigerator overnight.
To finish, lightly toast almonds in a skillet over medium-low heat until golden. Cool to room temperature. Using an electric mixer, whip the cream to stiff peaks, gradually beating in remaining sugar. Spread the whipped cream on top of the trifle. Sprinkle with toasted almonds and serve.