To make the starter
Mix the starter ingredients in a large bowl. Cover the bowl and let rest at room temperature for 1 hour. The mixture will initially be the consistency of thick pancake batter; after an hour it should be very bubbly, airy, and doubled in size.
While the starter rests, ready the dough. Melt the butter over low heat and set it aside to cool.
To make the sweet brioche
Mix 2 of the eggs into the risen starter. Stir in the cooled melted butter. Then stir in vanilla extract. Add sugar and stir until everything is incorporated.
Add the flour in three batches. The dough is going to be soft and sticky.
Let the mixer knead until the dough is gathered around the hook this will take about 10 minutes.
When dough is done, place the dough into a lightly greased bowl and cover with plastic wrap. Let dough rise for about 1 hour or until double in volume.
While the dough is rising, prepare the filling.
To make the Lemon Custard
Heat the milk over medium high heat and bring it to a simmer, almost to a boil.
While the milk is being heated, place the sugar, egg, lemon zest, cornstarch and salt in a bowl. Whisk until you have a thick, smooth mix.
As soon as the milk starts to bubble, remove it from the heat. Slowly whisk half of the hot milk with the egg to temper the mix. This keeps the egg from turning to scrambled eggs when you add them to the simmering milk.
Pour the egg/milk mixture back into the remaining simmering milk. Bring to a boil, stirring constantly with a whisk, until the mixture thickens.
Remove from the heat and add the butter and the vanilla extract. Whisk the butter, until it’s completely mixed in, then add lemon juice and whisk again.
Pour the custard into a bowl and immediately cover the surface with plastic wrap, making sure the plastic wrap is touching and sealing the whole surface. This is to prevent a custard skin from forming on top.
Let the custard cool down to room temperature and then let it chill in the fridge for a few hours until it’s completely chilled. With a hand mixer at medium speed, whip custard to become fluffy for about 1 minute, just before using it.
To make the braided brioche
Gently deflate the dough and divide it in half. Cover half with plastic wrap and set it aside as you roll out the first piece into a 10″ x 15″ rectangle. Rolling between two parchment papers makes moving the bread to the baking sheet much, much easier. Lightly press two lines down the dough lengthwise, to divide it into 3 equal sections. Spread half the lemon custard filling down the center section, and top with half the strawberry jam, leaving 1″ free on all sides of the filling.
To form the loaf, cut 1″ crosswise strips down the length of the outside sections, making sure you have the same number of strips down each side. Beginning on the left, lift the top dough strip and gently bring it across the filling diagonally. Repeat on the other side with the top dough strip, so that the two strips crisscross each other. Continue down the entire braid, alternating strips to form the loaf.
Repeat the rolling, filling, and braiding steps for the second piece of dough. Cover and let the loafs rise for about an hour or until double in volume.
Preheat the oven to 350°F/180°C. Brush the loaves with egg wash (one lightly beaten egg, 2 teaspoons water and a pinch of salt). Bake for 25 to 30 minutes or until the loaves are golden brown. Remove from the oven and cool for 15 to 20 minutes before serving.
Repeat the same instructions for making braided braid with chocolate hazelnut filling.
For the chocolate filling for two loafs
400 gr. / 14.10 oz. chopped chocolate of your choice
300 gr. / 10.58 oz. chopped hazelnuts
