Preheat oven to 350ºF. Combine cookie crumbs, sugar and butter in a 9” tart pan. Stir until crumbs are evenly moistened then press the mixture firmly into the bottom and up the sides of the pan using a flat-bottomed cup to push it down.
Bake for 12 minutes. Cool completely on a wire rack.
Place chocolate in a large heat-safe bowl.
Place cream in a microwave-safe bowl and microwave on high power for 1 ½ - 2 minutes until steaming hot and bubbles appear around the edges of the bowl.
Immediately pour the hot cream onto the chocolate and cover the bowl with a baking sheet or large plate and let stand 5 minutes to melt the chocolate.
Lift the cover, add the butter, and whisk to finish melting. If not completely melted, microwave on 50% power for 30-second intervals, stirring frequently, until smooth.
Pour into cooled shell and chill for 4 hours before serving.