Dough:
Melt the butter in a small saucepan over medium heat until it turns golden brown (about 5 minutes).
Let the butter cool to room temperature.

In a mixer with a paddle attachment, combine the milk, yeast, rum, and almond extract.
Add the eggs and mix.
While the mixer is running at low speed, add the flour, ground almonds, sugar, and salt.
Mix at low speed until the dough is homogeneous and has an elastic consistency, but is still sticky.
Slowly pour in the cooled butter and incorporate it.
Transfer the dough to a bowl, cover, and refrigerate overnight.

Transfer the dough to a lightly floured surface and cut it into 8 pieces.
Shape each piece into a ball and place them in a 9-inch (23cm) round cake pan previously greased.
Cover loosely and let rise for 1 hour.

Preheat the oven to 350°F (180°C).
Brush the tops of the brioche with the egg glaze.
Bake for 45 minutes or until the tops are golden brown.
Let cool completely in the pan.

Glaze:
Whip the powdered sugar and water until smooth and pipe a cross on each brioche using a piping bag.
The brioche is best served the same day, but it can also be frozen.