Somewhere between a soft cookie and a pound cake in texture, Gâteau Breton is a dense, buttery cake with a surprise layer of jam in the middle. Traditional versions from Brittany, France, where the recipe originates, are made with salted butter, but we use unsalted butter here to better control the level of salt in the cake. Plum or apricot jam are common fillings for this decadent dessert, but we enjoy a red raspberry jam for its tang and bright color — use whichever jam flavor you prefer!
To make the Gâteau Breton: In the bowl of a stand mixer fitted with the flat beater or in a large bowl working with an electric hand mixer, beat (“cream”) together the butter, sugar, and salt on high speed until pale and fluffy, about 3 to 4 minutes.
Add the yolks one at a time, pausing to turn the mixer off and scrape the bowl between additions, then add the vanilla. Beat on medium speed until smooth, about 1 minute.
Add the flour and baking powder and mix on low speed, just until incorporated, then scrape the sides of the bowl and mix briefly once more; the mixture should resemble soft cookie dough. (The dough can now be well wrapped and refrigerated for 3 to 5 days or frozen for up to 2 months. If frozen, thaw in the refrigerator overnight before using.)
To assemble the Gâteau Breton: When you’re ready to bake, transfer half of the dough (about 460g) to the pan. Wet the pads of your fingers, then use them to push the dough about 1/4" up the sides of the pan around the edge.
Transfer the pan, uncovered, to the freezer to chill for 15 minutes until firm. Meanwhile, preheat the oven to 350°F with a rack in the center.
Dollop the jam into the center of the dough and use a small offset spatula or the back of a spoon to spread the jam into an even layer, leaving a 1/2" border around the edge bare.
Return the pan, uncovered, to the freezer for 10 minutes to chill. (The jam will still be wet and sticky after this rest; it won’t freeze solid.)
Press the remaining dough between your fingertips into flat pieces about 3/8" thick and roughly 1" to 2" across and place them on top of the jam filling. (Exact size is less important here than covering the entire surface from edge to edge with dough that can be smoothed into an even surface.)
Dip a small offset spatula in water to help prevent the dough from sticking, then use it to smooth the dough into an even layer, completely covering the jam.
Return the pan, uncovered, to the freezer one last time to chill for 10 minutes.
In a small bowl, whisk together the egg wash ingredients.
Remove the cake from the freezer and brush a thin layer of egg wash evenly over the surface (this gives the cake a shiny, golden brown top). Use the tines of a fork to score a decorative diagonal or crisscross pattern on the surface.
Bake for 50 to 60 minutes, or until the top is golden brown and the surface feels firm when pressed gently.
Remove the cake from the oven and transfer to a wire rack to cool for about 1 hour. Run a small offset spatula or butter knife around the edge to loosen the sides. Invert the cake onto a plate and then invert once again onto a serving plate. Cut into slices and serve slightly warm or at room temperature.
Storage information: Store leftover Gâteau Breton in an airtight container at room temperature for up to 1 week; freeze for longer storage.
Tips from our Bakers
To freeze the Gâteau Breton before baking: Freeze the fully assembled, unbaked, and egg-washed cake directly in the pan. Let the cake thaw in the refrigerator overnight before scoring and baking according to the recipe instructions.
To freeze the Gâteau Breton after baking: Let the cake cool completely, then wrap it in a layer of plastic wrap or your favorite reusable wrap, followed by a layer of foil. When ready to eat, thaw at room temperature for 3 to 4 hours. Once thawed, the whole cake can be warmed slightly in the oven at 350°F for 10 minutes before serving.
