Roughly crush 12 gingersnaps, 6 whole graham crackers and 5 shortbread cookies, then pulse in a food processor until finely ground. Add 3 tablespoons cold water and pulse until combined, then let sit 10 minutes. Add 1/4 cup sugar, 1/2 teaspoon vanilla and a pinch of cinnamon. With the processor running, slowly drizzle in 1/2 cup coconut milk and blend until smooth. Refrigerate in an airtight container for up to 2 weeks.