Butter and/or parchment an 8 inch cake pan and preheat the oven to 350 degrees.
In a bowl, combine the flour and sucanant. Whisk to combine.
Add in the butter, egg yolks, rum, and vanilla seeds. Use your hands to gently combine the mixture. Don’t knead the dough, but rather, lovingly and gently work your fingers through the ingredients until it’s all incorporated together.
Transfer the dough to the cake pan and use your fingers to gently press the dough evenly into the pan, reaching all the sides of the pan evenly.
Lastly, combine the additional egg yolk and cream together in a small bowl before brushing it over the top of the cake. Score the top with a fork, if desired (because that’s what they do in Brittany and it’s pretty!).
Bake for 30-35 minutes, until deeply golden. Let it rest for a few minutes before removing it to a wire rack to cool.