Prepare the soaking liquid: In a shallow dish, combine the cooled coffee/espresso and the Amaretto (if using). Set aside.

Make the mascarpone cream: In a large bowl, beat the cold heavy whipping cream until stiff peaks form. Set aside.

In a separate bowl, gently whisk together the room temperature mascarpone cheese, sifted powdered sugar, vanilla extract, and lemon juice until smooth and creamy. Do not overmix.

Fold the whipped cream into the mascarpone mixture in two additions until just combined and light. Be careful not to deflate the mixture.

Assemble the Tiramisu: Quickly dip both sides of each ladyfinger into the coffee mixture—do not oversoak. Arrange a single layer of dipped ladyfingers in the bottom of an 8x8 inch dish.

Spread half of the mascarpone cream evenly over the first layer of ladyfingers. Top evenly with half of the 3 cups of mixed berries.

Repeat the layers: Top with another layer of soaked ladyfingers, the remaining mascarpone cream, and the rest of the mixed berries.

Chill for at least 4 hours, or preferably overnight, to allow the flavors to meld and the structure to set.

Before serving, garnish with the remaining fresh berries and dust lightly with powdered sugar.