First, wash the glacé cherries under cold water to remove the syrup then leave to drain on a piece of kitchen paper.
Preheat an oven to 180°c/160°c fan (356°f/320°f).
Grease a 2 lb loaf tin with butter then line the bottom & two longer sides with a piece of baking parchment, leaving a couple of centimetres overhanging the tin's edges (this makes it easier to take the cake out of the tin once it is cooked!).
Next, add the caster sugar into the bowl of a stand mixer then add in the lemon zest. Use your fingers to rub the zest into the sugar then add in the softened butter.
Beat the butter on a medium speed (with the paddle attachment) for 4-6 minutes, until pale and fluffy. Make sure to scrape the bowl down regularly with a spatula.
Whilst the butter is mixing, crack the eggs into a jug then add in the vanilla & almond extracts and beat lightly with a fork. Sift the flour & baking powder into a separate bowl then add in the ground almonds & salt and whisk to combine. Then finally, chop the cherries into small pieces, add into a mixing bowl and mix with 1 tbsp of plain flour, to coat.To prevent the cherries from sinking, chop them into 6-8 pieces depending on their size. Next, gradually pour the eggs into the butter, with the mixer still running on a medium speed. Once all the eggs have been added, give the bowl another scrape down then mix again for a minute.Make sure to mix the eggs in gradually, to keep the batter from splitting. Next, take the bowl off the mixer then add in half of the flour and fold in gently (with a spatula) until just combined. Add in the remaining flour & the sour cream then fold again, until just incorporated.
Add ¾ of the cherries into the batter then fold gently, to evenly distributed. Then transfer the cake batter into the lined tin, spreading it out gently into an even layer with a spatula. Place the remaining cherries on top, leaving a space in the middle for the butter to go.
Pipe a thin line of softened butter straight down the middle of the cake, sprinkle over the demerara sugar then bake in the preheated oven for 55 minutes – 1 hour, until golden brown & a skewer inserted into the centre comes out clean.Piping butter down the middle of the cake lets us control how the top of the cake cracks as it bakes – this is optional though! If your cake starts to brown too much towards the end of the bake, cover the top loosely with foil. Once baked, let the cake cool in the tin for 30 minutes then run a small palette knife along each end & carefully lift it out of the tin (using the overhanging parchment). Transfer to a wire cooling rack, to cool completely.
If you've got the time, you'll get the best flavour by wrapping the cake in clingfilm and letting it mature overnight before serving. It'll still taste great if served straight away though!