Gateau Nantais

Preheat the oven to 350°F (175°C).

Grease an 8-inch (20 cm) round cake pan with ½ teaspoon of the butter and dust the bottom and sides with 1 tablespoon of the all-purpose flour. Tap out the excess.

In a bowl, combine the almond flour, remaining all-purpose flour, and salt. In a medium bowl, combine the remaining butter and the sugar. Add in the vanilla and cream everything together. Whisk in the eggs, one by one, beating well between each addition. Whisk in the rum. Fold the dry ingredients into the wet without overmixing; the batter will be thick. Pour the batter into the prepared pan and tap it against the counter to settle. Bake until the top of the cake is golden and a cake tester inserted into the center comes out clean, 25 to 30 minutes.