Mile High Ice Cream Pie

Make the ice cream pie Line a large stainless steel bowl with plastic wrap, leaving a 3-inch overhang. Using a rubber spatula, scrape the softened mint chip ice cream into the prepared bowl and smooth the surface. Freeze until very firm, about 1 hour. Scrape the softened vanilla ice cream into the prepared bowl and smooth over the mint chip ice cream. Freeze until very firm, about 1 hour. Scrape the chocolate ice cream into the prepared bowl and smooth over the vanilla ice cream. Freeze until very firm, about 1 hour more. 

In a medium bowl, mix the crushed wafer cookies with the melted butter and the salt until the cookie crumbs are evenly moistened. Spread the cookie crumble in an even layer over the chocolate ice cream and, using the bottom of a glass or measuring cup, pack it into a firm layer. Fold the plastic wrap overhang over the cookie crust and freeze overnight.

Make the meringue In a medium saucepan, bring 2 inches of water to a simmer. In the bowl of a stand mixer, whisk the egg whites with the sugar. Set the bowl over the saucepan (the bowl should not be touching the water) and cook, whisking constantly, until the sugar is completely dissolved and an instant-read thermometer inserted into the egg whites reads 160°, about 5 minutes. Attach the bowl to a stand mixer fitted with a whisk attachment and beat at medium-high speed until the meringue is thick, white and glossy, 5 to 7 minutes. Meanwhile, unwrap the pie and carefully invert onto a platter or cake stand; discard the plastic wrap. Using an offset spatula, swirl the meringue all over the pie. Freeze until set, about 20 minutes. 

Meanwhile, make the chocolate sauce Bring the saucepan with 2 inches of water to a simmer. Place the chocolate in a heatproof medium bowl and set over the saucepan. The bowl should not be touching the water. Cook, stirring occasionally, until the chocolate is melted, about 5 minutes. Remove the bowl from the heat and whisk in the corn syrup and boiling water. Scrape the chocolate sauce into a serving bowl and let cool slightly, about 20 minutes. 

Let the pie stand at room temperature for 10 minutes, then cut into thick slices and serve immediately with the warm chocolate sauce.