- For the cake, preheat the oven to 350° F (180° C). Line a baking tray (11-x-17-inches/28-x-43-cm) with parchment paper, but do not grease the pan.
- Sift the flour, sugar, cocoa powder, baking soda and salt into a large mixing bowl or into the bowl of a stand mixer fitted with the paddle attachment. Add the butter cutting it in (if in a large bowl, use electric beaters) until the mixture is a fine crumble (like the texture of fine breadcrumbs) and no large pieces of butter are visible.
- Stir the hot coffee, milk and vanilla together and add it all at once to the flour mixture, blending until smooth. Break the eggs into a small dish and stir them with a fork and then add them to the batter, again blending on medium speed just until smooth (the batter will be very fluid). Pour the batter into the prepared pan, spreading it evenly and bake for about 25 minutes, until a tester inserted in the centre of the cake comes out clean. Cool the cake in its pan.
- For the white chocolate pastry cream, heat the milk with the scraped seeds of the vanilla bean or the vanilla bean paste until just below a simmer.
- In a separate bowl, whisk the egg yolks, sugar and cornstarch. Ready a bowl with the white chocolate and butter, placing a strainer on top of it.
- Gradually whisk the hot milk into egg mixture and then return it all to the pot. Whisk this constantly (switching to a spatula now and again, to get into the corners) over medium heat until thickened and glossy, about 2 minutes. Pour this immediately through the strainer, whisking it through if needed, and stir in the white chocolate and butter. Place a piece of plastic wrap directly over the surface of the custard, cool to room temperature and then chill completely until ready to use.
- For the poached pears, peel the pears, cut them in half, core them and remove the stems. Bring the water, sugar, lemon juice and scraped seeds from the vanilla bean (or vanilla bean paste) up to a full boil. Add the pears and cover them directly on the surface of the liquid with a piece of parchment paper cut to fit the pot (called a cartouche). Return the pears to a gentle simmer and simmer for 10 minutes. Then remove the pot from the heat and let the pears cool to room temperature in the syrup before chilling until ready to assemble.
- For the ganache, heat ½ cup (125 mL) of the whipping cream to a simmer and pour this over the chocolate in a small bowl. Gently stir the mixture until the ganache is smooth and cool to room temperature. Whip the remaining 1 cup (250 mL) of cream with the sugar and chill until ready to assemble.
- To assemble, have ready a 12-cup (3 L) trifle bowl or glass vessel. Turn the chocolate cake out onto a cutting board, peel away the parchment paper and cut 3 to 4 pieces of cake that are the size of your trifle bowl. Remove the pears from the vanilla syrup (but save the syrup for brushing onto the cake) and cut them into ½-inch (12 mm) slices, saving one pear half for the top of the trifle.
- Start by placing a layer of cake in the bottom of the bowl. Brush this generously with vanilla syrup and top the cake with a layer of the white chocolate pastry cream. Drizzle the cream with a little chocolate ganache and arrange pear slices overtop. Repeat this with the cake, syrup, cream and pear until the cake layers are used and you’ve finished with a layer of pear slices. Top this with the whipped cream, and chocolate shavings. Slice the final pear half so that it fans out from the stem and place this on top. Chill the trifle until ready to serve.
The trifle can be prepared and assembled a day in advance.