Step 1
Mix water yeast and 1 tablespoon sugar together in a small bowl until yeast is raised and bubbly 5 to 10 minutes.
Step 2
Cream butter and 1 cup sugar together in the bowl of an electric stand mixer. Pour in warm milk and add yeast mixture eggs and salt; mix together. Mix in flour until just incorporated; do not knead dough.
Step 3
Move dough to a large bowl and cover with a towel. Let rise until doubled in size about 1 1/2 hours. Punch dough down and let rise for another 45 minutes.
Step 4
While dough is rising heat milk for pastry filling in a medium saucepan until warm 2 to 3 minutes. Whisk in 3 tablespoons flour gradually. Beat egg yolk in a separate bowl and add a little of the warm milk mixture to temper it; whisk yolk mixture into milk mixture. Mix in sugar and salt. Cook until thickened stirring constantly about 5 minutes.
Step 5
Let cool to room temperature about 5 minutes. Cover the top with plastic wrap touching the filling to prevent skin from forming. Refrigerate until cool 20 to 30 minutes.
Step 6
Meanwhile make almond filling by mixing butter sugar and almond extract together in a bowl until blended. Set aside.
Step 7
Make nut crumb filling by crumbling flour sugar walnuts and butter together in a bowl. Set aside.
Step 8
Preheat the oven to 375 degrees F (190 degrees C). Line 2 half sheet pans with parchment paper or silicone mats.
Step 9
Divide the dough and fillings in 1/2 for 2 loaves. Set aside a small amount of nut filling to sprinkle on top of loaves.
Step 9
Roll out 1/2 of the dough onto 1 of the prepared pans into a rectangle that fills the pan. Spread cream filling lengthwise down the middle 1/3 of the dough leaving about 1 inch free on each short end. Sprinkle almond filling on top of cream followed by nut crumb filling.