Step 1: If using fresh peaches, peel, pit, and slice them about 1/4-inch thick. If using canned, drain thoroughly. Gently wash raspberries; set aside about 1/4 cup for garnish.
Step 2: In a small saucepan, combine the remaining raspberries, 2 tablespoons of sugar, and 1 tablespoon of water. Bring to a gentle simmer over medium heat, stirring occasionally, until raspberries break down and sauce thickens (5-7 minutes). Press mixture through a fine-mesh sieve to remove seeds, creating a smooth coulis. Let cool completely.
Step 3: In a large mixing bowl, beat softened cream cheese with 1/2 cup granulated sugar and vanilla extract until smooth and creamy, about 2-3 minutes.
Step 4: In a separate, chilled bowl, whip the cold heavy cream until soft peaks form. Be careful not to over-whip.
Step 5: Gently fold about one-third of the whipped cream into the cream cheese mixture to lighten it, then fold in the remaining whipped cream until just combined. Do not overmix.
Step 6: Spread a thin layer of the cream mixture on the bottom of a 9×13 inch baking dish. Arrange a single layer of vanilla wafers over the cream, breaking some if necessary to fit.
Step 7: Spread about one-third of the remaining cream mixture over the wafers. Arrange half of the sliced peaches evenly over the cream. Drizzle about a third of the cooled raspberry coulis over the peaches.
Step 8: Repeat the layering: another layer of vanilla wafers, followed by another third of the cream mixture, the remaining peaches, and another third of the raspberry coulis.
Step 9: Finish with a final layer of vanilla wafers, topped with the remaining cream mixture. Smooth the top with a spatula. Drizzle the remaining raspberry coulis over the top in an attractive pattern; use a skewer to swirl if desired.
Step 10: Cover the dish tightly with plastic wrap and refrigerate for at least 6 hours, or preferably overnight, to allow the wafers to soften and flavors to meld.
Step 11: Before serving, garnish your Peach Melba Icebox Cake with the reserved fresh raspberries and a few extra peach slices or mint leaves. Cut into squares and serve cold.