1 pound (4 sticks) unsalted butter, softened
1/2 cup blackberries
1/2 cup raspberries
1 loaf crusty bread, such as baguette, French loaf, etc.
4 whole egg yolks
2 cups half-and-half
1 tablespoon sugar
2 teaspoons vanilla extract
Zest of 1 lemon
Butter, for frying
Sifted powdered sugar, for serving, optional
Maple syrup, warm, for serving