Take a sheet of greaseproof paper and draw a 10cm x 10cm square on it, turn the square over and place the 225g butter in the middle of it. Using a stepped palette knife spread the butter into an even layer so that it fills the square.
Use the knife to neaten the edges and corners, wrap the square up in the greaseproof paper and then wrap in cling-film and place it in the fridge to firm up.
Place the 25g of butter, both types of flour and salt in the bowl of a stand mixer fitted with the paddle attachment. Mix on a low speed until it resembles breadcrumbs.
Add the water and mix again until it starts to form a dough.
Tip the dough onto a surface that is clean and knead it until it all comes together and begins to look smooth and a bit elastic.
Shape the dough into a ball and cut a cross in the top of it. Wrap the dough in cling-film and let it rest in the fridge for an hour.
Take the dough out of the fridge and place it on a lightly floured surface. Roll out the dough from each cut edge until it looks like a diamond that will be big enough to encase the butter block (beurrage).
Place the butter block on the pastry and pull up the triangles to encase the dough like an envelope.
Press the dough together with your fingers so that the butter is completely encased.
Roll the pastry out into a rectangle that is three times as long as the width. Fold the top third of the dough over, using a pastry brush, brush off any excess flour and then fold the bottom third up to cover the top third, again brushing off any excess flour.
Turn the dough 90 degrees so that the folded edge is on the left or right now.
Roll the dough out again to a size that is three times as long as the width and then fold the top third of the dough over, using a pastry brush remove any excess flour.
Fold the bottom third of the dough over the top and again brush off any excess flour.
Wrap the dough in cling-film and place in a Zip lock bag to stop any moisture getting to the pastry and let it rest in the fridge for an hour.
After an hour take the pastry out of the fridge and repeat the last four steps twice more, this will mean you have completed 6 turns in 3 batches.
Place the dough in the fridge to chill for another hour.
When the dough is chilled, cut it into two blocks one that is a third in size and one that is two thirds.
Take the larger block of pastry and place it back in the fridge. Roll out the smaller piece of pastry on a floured surface and cut out a circle that is 22cm in diameter. Place this round of pastry back in the fridge on a piece of greaseproof paper.
Take the larger block of pastry and roll it out on a floured surface, cut out a circle that is 24cm in diameter.
Place this round of pastry back in the fridge on a piece of greaseproof paper.
Next make the filling, melt the chocolate in a bain-marie and then place to one side.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and sugar together.
Add the egg and the egg yolk and beat until combined, then add the ground almonds and mix until combined.
Then using a spatula scrape in the melted chocolate and add the dark rum, gently stir it into the frangipane mixture. When it is all combined, place the chocolate frangipane in a disposable piping back and place to one side.
Preheat the oven to 160C Fan/180C and place the smaller circle of pastry on a baking tray with the greaseproof paper still underneath. Pipe a spiral of the chocolate frangipane onto the ring of dough, leaving 2cm from the edge of the pastry. If you don’t use all the frangipane, just pipe it on top starting from the middle, you want an almost dome like shape.
Take the egg wash and using a brush, spread it around the exposed edge of the bottom piece of pastry.
Take the larger ring of pastry out of the fridge and place it gently over the bottom half of the galette des rois. Press the edges together and crimp them so that the galette will not come apart when cooking.
Brush the galette with the rest of the egg wash and place it back in the fridge for 15 minutes.
Take the galette out of the fridge and then using a small sharp knife score any pattern you want into the top of the galette, be careful not to cut all the way through the pastry, you don’t want any filling to spill out.
Place the galette in the oven and bake for 35-45 minutes until it is golden.
Remove the galette from the oven and leave to firm up on the tray for 30 mins before transferring to a wire rack and leaving to cool.
This keeps well, but does taste best on the day of baking.