In the top of a double boiler, whisk together all ingredients. Cook over simmering water, whisking constantly, until sugar is dissolved and mixture registers 140°F (60°C) on a candy thermometer, 5 to 7 minutes.
Transfer mixture to the bowl of a stand mixer fitted with the whisk attachment; beat at high speed until stiff peaks form, about 10 minutes. Use immediately.
Notes
PRO TIP
Substitute any of your favorite crisp cookies for the gingersnaps in this crumb crust. The recipe method will stay the same, but you may have to adjust the amount of butter and sugar if the cookie has a different sugar or fat content than gingersnaps. Add the sugar to taste, and add the butter gradually, mixing only until crumbs are slightly moist.