In a bowl, combine the milk, sugar, salt, and butter. Stir until the sugar and salt are dissolved. Warm the mixture in the microwave until it becomes lukewarm. Remove from the microwave and add the egg, beating it several times until well blended.

In a large bowl, mix together the flour and yeast. Pour the liquid mixture over the flour and mix until a dough forms. Knead the dough on a clean, floured surface until it becomes smooth and elastic, which should take about 7-10 minutes.

Form the dough into a ball and place it in a greased bowl. Cover the bowl with a kitchen towel or plastic wrap and place it in a warm area to let it rise until it doubles in size. This could take anywhere from 30 minutes to an hour or longer, depending on the temperature.

Once the dough has risen, punch it down and divide it into 4 equal parts using a knife or dough slicer. Roll each part into a 6-inch long log. Arrange the pieces on a baking sheet and cover them with a clean kitchen towel. Allow them to rise for another 10-15 minutes. Meanwhile, preheat the oven to 370°F (185°C).

Bake the dough for 15 minutes or until the sides turn slightly brown. Remove from the oven and let it cool down. Cut each piece into 4 equal parts lengthwise.

Place the pieces in a bread box or simply cover them with a dry kitchen towel. Leave them at room temperature for a day or two (or longer) to dry out and harden. Alternatively, you can proceed to the next step without drying them out, but adjust the baking time accordingly.

Preheat the oven to 150°C.

Arrange the pieces on a baking sheet lined with parchment paper. Brush a thin layer of softened butter or margarine on the cut sides of each piece. Next, generously brush them with condensed milk.

Bake for 20-30 minutes or until the edges turn slightly golden and the condensed milk becomes glossy but no longer tacky. The bread should also dry out and become crunchy.