Upside-down caramel apple and cider cake with buttermilk custard

For cinnamon buttermilk custard, place cream and cinnamon in a saucepan and bring to a simmer over medium heat. Remove from heat and stand to infuse (15 minutes). Whisk yolks and sugar in a bowl until pale and thick, then pour over cream mixture and whisk to combine. Return to pan and stir continuously until mixture thickly coats the back of a wooden spoon (5-6 minutes). Strain into a clean bowl, return cinnamon quills, cover and refrigerate overnight to infuse. Discard cinnamon, then whisk in buttermilk to combine; refrigerate until required.

Preheat oven to 160°C fan-forced. Grease and line a 22cm-diameter cake tin with baking paper.

For caramel apple topping, place sugar in a small saucepan over medium high heat. Cook, swirling pan, until a dark caramel forms (3-5 minutes). Remove from heat, add butter, swirl to combine and pour into prepared cake tin. Thinly slice apple on a mandolin, toss in melted butter and arrange, overlapping slightly, over caramel. Set aside.

For cake, combine apples, lemon zest and juice in a bowl and toss to combine; stand to macerate (15 minutes). Sift flours, baking powder and cinnamon into a bowl. Beat butter and sugar in an electric mixer until pale and fluffy, scrape down sides of bowl, then beat in eggs, one at a time, beating well and scraping down sides of bowl between additions. Add flours and cider alternately in 3 batches, beating until just combined, then beat in vanilla. Transfer cake batter to a large bowl and fold through macerated apples. Spoon into prepared tin. Tap tin on bench to remove air bubbles, smooth top and bake until golden brown and a skewer inserted withdraws clean (50 minutes – 1 hour). Cool in tin for 10 minutes, then invert onto a cake rack to cool.

Meanwhile, for hazelnut streusel crumb, place all ingredients except hazelnuts in a bowl and using your fingertips, rub in butter until clumps form. Stir in hazelnuts and spread mixture over an oven tray lined with baking paper and bake until golden (15-20 minutes). Cool completely and coarsely crumble. Store in an airtight container for 1 week.

Serve cake scattered with streusel crumb and drizzled with custard.