• Preheat oven to 350°F. Lightly grease a 9-inch springform pan, then put a kettle of water on or boil a large pot of water.

Oreo Crust

• In bowl, stir together Oreo cookie crumbs and melted butter until moistened; press evenly onto base of prepared springform pan using bottom of measuring cup. Bake until set, about 8 minutes. Reduce oven to 300°F. Let crust cool completely. Wrap pan with large square heavy-duty foil to cover bottom to top edge.

Chocolate Orange Cheesecake

• While crust is cooling, beat cream cheese on medium in bowl of stand mixer fitted with paddle attachment until smooth. Gradually beat in sugars, scraping down sides of bowl, until smooth. Add sour cream, vanilla, orange oil and orange zest, and beat on medium-low until combined, scraping bottom and sides of bowl.
• On low speed, beat in eggs and then melted chocolate, scraping the bowl. Do not overmix or the batter will contain too much air, which can cause bubbles and cracks. Pour over crust, smoothing top with offset spatula. Firmly tap pan on counter to pop any air bubbles.
• Place pan in a broiler pan or roasting pan. Place in centre of oven and pour enough boiling water into broiler pan to come about 1 inch up side of foil-wrapped springform pan. Bake until surface is no longer shiny and edge of cheesecake is set yet centre is still jiggly, about 70 minutes.
• Remove cheesecake from oven and let cool completely on rack. Cover pan without touching cheesecake, and refrigerate at least 4 hours or overnight. Gently blot any condensation that forms on surface with paper towel.

Ganache Glaze

• In saucepan, heat cream until almost simmering. Remove from heat; add chocolate and let stand 1 minute. Gently whisk until smooth; pour on top of cake and spread to edge. Refrigerate to set.
• Run a paring knife dipped in hot water around edge of cheesecake to loosen from pan. Remove collar.
• Garnish with candied orange slices on top, if desired.