Method

• 1.
  Preheat oven to 180°C or 160°C fan-forced. Trim the 3 lemons, slicing and discarding the tips, then cut each lemon into very thin (2mm thick) rounds to get 24 slices. Discard the seeds. Place a large non-stick pan over high heat. Working in about 3 batches, add lemon slices in a single layer and cook until nicely charred on both sides, 1-2 minutes per side. Repeat with the remaining slices and set aside.
• 2.
  Line a baking dish about 20cm x 30cm in size with a piece of baking paper large enough to cover the base and sides, and enough overhang to later fold over the batter. Pour 1/2 cup (125ml) maple syrup into the prepared dish. Halve the vanilla bean lengthwise, scrape the seeds into a small bowl, then add the pod to the prepared dish. Top with the charred lemon slices, spreading out so they cover the entire base while overlapping slightly in spots.

• 3.
  Sift the flour, baking powder and salt into the bowl of a stand mixer fitted with the whisk attachment, and whisk on medium speed to combine. Add the room-temperature butter, eggs and egg yolk, brown sugar, milk, reserved vanilla seeds and the extra 3 tbs maple syrup, and mix on medium-low speed for 2 minutes until combined. The mixture will look like it’s split a little with some smaller cubes of butter, but that’s okay.
• 4.
  Spoon mixture into a piping bag or resealable plastic bag, snipping the base, and pipe mixture directly on top of lemons in the baking dish in an even layer (this ensures the lemons don’t move around too much). Using the back of a spoon, smooth over the mixture to create an even layer. Fold over the excess baking paper to cover, then wrap the dish tightly in foil.
• 5.
  Place the baking dish into a larger roasting pan roughly 24cm x 36cm. Carefully add about 3cm of boiling water to the pan, transfer to the oven and bake for 1 hour-1 hour 10 minutes until a toothpick inserted into the centre comes out clean. Lift the baking dish from the water, remove foil and baking paper. Set aside for 5 minutes before carefully inverting onto a platter, carefully removing baking paper to expose the lemons.
• 6.
  During the final 10 minutes of baking, prepare the lemon-maple butter: add the lemon juice and maple syrup to a small saucepan and bring to a simmer over medium-high heat. Cook for about 2 minutes, then turn down heat to low. Once the mixture is no longer simmering, gradually whisk in chilled butter a little at a time until you have an emulsified sauce.
• 7.
  Drizzle half the lemon-maple butter all over the warm sponge cake and serve warm, with the remaining lemon-maple butter and creme fraiche alongside.