Cream the Butter and Sugar: Start by beating the softened butter and sugar together in a large bowl until light and creamy. This is the foundation of that classic rich texture, so take your time—3 to 4 minutes should do it.

Add the Egg Yolks and Vanilla: Add the egg yolks one at a time, mixing well after each addition. Then stir in the vanilla extract. The yolks are key to the cake’s signature richness and golden hue.

Fold in the Dry Ingredients: Sift the flour and salt together, then gradually add to the butter mixture. Use a spatula or wooden spoon to combine—don’t overmix. The dough will be thick, like a soft cookie dough.

Transfer to Pan: Grease and line the bottom of an 8-inch cake pan with parchment paper. Press the dough evenly into the pan, smoothing the top with the back of a spoon or your fingers.

Glaze and Score: Mix the remaining egg yolk with milk and brush it over the top of the dough. Use a fork or knife to lightly score a crisscross pattern—a traditional look for this rustic French cake.

Bake: Bake at 350°F (175°C) for 35–40 minutes, or until the top is golden and the edges are slightly crisp. A toothpick inserted should come out clean, but remember—the inside will be dense and buttery, not fluffy like a sponge cake.

Cool and Serve: Let the cake cool in the pan for about 15 minutes before transferring to a wire rack. Slice once fully cooled and enjoy with a warm drink or a dollop of whipped cream, if you like.