MAKE THE PORT WINE SYRUP (Can Be Done Ahead)
1. Combine the port wine, sugar, orange zest strips, cinnamon stick and cloves in a small saucepan. Bring to a boil over medium heat, stirring until the sugar dissolves.
2. Reduce the heat and simmer until the liquid has reduced by about half and become syrupy — roughly 12–15 minutes. It should coat the back of a spoon.
3. Remove from heat, stir in the orange juice, and strain out the solids. Set aside to cool completely. The syrup can be made up to 3 days ahead and refrigerated; bring to room temperature before using.

BAKE THE ORANGE AND OLIVE OIL SPONGE
4. Preheat the oven to 175°C (350°F). Line a 9 × 13-inch baking pan with parchment paper, leaving overhang on the long sides for easy removal. Lightly grease the parchment.
5. Whisk the dry ingredients together in a large bowl: flour, sugar, baking powder, baking soda, salt and cinnamon.
6. In a separate bowl or jug, whisk together the eggs, olive oil, milk, orange juice, orange zest and vanilla until well combined.
7. Pour the wet ingredients into the dry and fold gently with a spatula until just combined — no dry streaks should remain, but do not overmix. The batter will be quite liquid compared to a butter cake; this is correct and will produce the moist, tender crumb characteristic of Portuguese-style olive oil cakes.
8. Pour into the prepared pan and bake for 30–35 minutes, until the cake is golden, springs back when lightly pressed, and a skewer inserted into the centre comes out clean.
9. While the cake is still warm, poke holes across the surface using a skewer or fork (roughly every inch) and brush generously with about two-thirds of the port wine syrup, allowing it to soak in. Reserve the remaining syrup for glazing or serving. Let the cake cool completely in the pan on a wire rack.

MAKE THE PORT WINE REDUCTION (For the Buttercream)
10. In a small saucepan, simmer 120ml (½ cup) of port wine over medium-low heat until reduced to approximately 3 tablespoons — thick, syrupy and deeply concentrated, about 10–12 minutes. Watch carefully in the final minutes as it can scorch. Cool completely.

MAKE THE PORT WINE AND ORANGE CUSTARD BUTTERCREAM
11. Combine the sugar and water in a small saucepan. Stir to dissolve, then cook over medium-high heat without stirring until it reaches 116°C (240°F) on a candy thermometer — the soft-ball stage.
12. Meanwhile, beat the egg yolks in a stand mixer with the whisk attachment on medium-high speed until pale, thick and doubled in volume, about 3–4 minutes.
13. With the mixer running on medium speed, carefully drizzle the hot sugar syrup down the side of the bowl in a thin, steady stream (avoid hitting the whisk or it will splatter). Once all the syrup is added, increase to high speed and beat until the mixture is completely cool to the touch and very thick — about 8–10 minutes.
14. Switch to the paddle attachment. With the mixer on medium speed, add the softened butter one cube at a time, beating well after each addition. The mixture may look curdled at some point — this is normal. Keep beating and it will come together into a silky, smooth buttercream.
15. Beat in the cooled port wine reduction, orange zest, vanilla and salt. The buttercream should be a beautiful pale mauve with a pronounced port wine fragrance. Taste and adjust — a tiny pinch more salt can help the port flavour bloom.

MAKE THE DARK CHOCOLATE AND PORT GLAZE
16. Place the chopped chocolate in a heatproof bowl.
17. Heat the cream in a small saucepan until it just begins to simmer. Pour over the chocolate and let sit for 1 minute, then stir from the centre outward until completely smooth.
18. Stir in the port wine, butter and orange zest until glossy and uniform. Let cool until it reaches a thick but still pourable consistency — about 10–15 minutes at room temperature.

ASSEMBLE THE CAKE
19. Level the cooled, syrup-soaked cake if necessary by trimming the top with a long serrated knife to ensure perfectly uniform pieces.
20. Spread the port wine and orange custard buttercream in an even layer across the top of the cake — about 6mm (¼ inch) thick. Use an offset spatula for a smooth finish. Refrigerate for 15 minutes to firm.
21. Pour the chocolate-port glaze over the buttercream layer, tilting the pan gently to encourage even coverage. Use an offset spatula to smooth if needed.
22. Immediately scatter the toasted sliced almonds and diced candied orange peel across the surface while the glaze is still tacky. Finish with the lightest pinch of flaky sea salt.
23. Refrigerate for at least 30 minutes to set the glaze fully.

CUT AND SERVE
24. Using the parchment overhang, lift the entire cake from the pan onto a cutting board.
25. Using a long, sharp knife dipped in hot water and wiped clean between cuts, score the cake into a 4 × 4 grid to yield 16 identical pieces. Cut cleanly through the markings.
26. Serve at cool room temperature — the buttercream and glaze should be firm enough to hold their shape but soft enough to yield pleasantly when bitten. Drizzle any remaining port wine syrup around each piece on the plate if desired.