Here’s a clear, rephrased step-by-step process for making the cake:

1. Make the apple puree. Peel, core, and roughly chop the apples. Place the apples, lemon juice, and caster sugar into a saucepan and stir to combine. Bring to a gentle bubbling over medium heat, then cover and simmer on low for about 10 minutes—or until you can mash the apples easily into a rough puree. You should end up with about 285 g (a generous cup) of puree. Set aside to cool.
2. Prepare your tin. Preheat your oven to Gas mark 4 (180 °C / 160 °C fan / 350 °F). Lightly oil a 25 cm (10‑inch) springform tin with vegetable (or almond, if preferred) oil and line the bottom with baking parchment.
3. Blend the batter. Into a food processor, add the cooled apple puree, eggs, ground almonds, caster sugar, and the squeeze of lemon juice. Blitz until completely smooth.
4. Bake. Pour the batter into the prepared tin, scraping down the sides with a rubber spatula. Scatter the flaked almonds evenly over the top. Bake for approximately 45 minutes—but begin checking at around 35 minutes since oven temperatures vary. The cake should be golden on top, and a skewer inserted into the center should come out mostly clean.
5. Cool and serve. Place the tin on a wire rack, allow it to cool slightly, then unlock and remove the springform. The cake is divine when served slightly warm, though it remains delicious served cold. Just before serving, dust the top lightly with icing sugar through a fine sieve.