01 - Combine peach wedges, lemon juice, and 2 tablespoons sugar in a large mixing bowl. Toss gently to coat evenly. Let stand at room temperature for 10 minutes, allowing fruit to macerate and release natural juices.
02 - Using a hand mixer or stand mixer fitted with the whisk attachment, beat the cold heavy cream on medium-high speed until soft peaks form. Do not overbeat. Set aside.
03 - In a separate medium bowl, combine softened mascarpone cheese, 1/3 cup sugar, and vanilla extract. Beat with an electric mixer or whisk until completely smooth and creamy, approximately 2 minutes.
04 - Gently fold one-third of the whipped cream into the mascarpone mixture to lighten it. Add remaining whipped cream and fold in using a rubber spatula with a gentle lifting motion until fully incorporated and no white streaks remain.
05 - Whisk together peach nectar and peach schnapps (if using) in a shallow dish wide enough to accommodate ladyfingers.
06 - Working quickly, dip each ladyfinger into the peach liquid for just 1-2 seconds per side. The cookies should be moistened but not saturated or soggy.
07 - Arrange 12 dipped ladyfingers in a single snug layer at the bottom of a 9x7 inch serving dish. Spread half the mascarpone cream evenly over cookies using an offset spatula. Top with half the macerated peach slices, arranging in an even layer.
08 - Repeat with remaining dipped ladyfingers, spreading the rest of the mascarpone cream over top. Finish with remaining peach slices, distributing evenly. Cover dish tightly with plastic wrap.
09 - Refrigerate for minimum 4 hours or preferably overnight. The extended chilling time allows flavors to develop and texture to set properly.
10 - Just before serving, remove plastic wrap and garnish with fresh mint leaves. Cut into squares and serve chilled directly from the baking dish.