Put water, salt, sugar, and yeast into a mixing bowl and stir until the yeast is dissolved. Add the flour gradually until the dough pulls away from the sides of the bowl. Give the dough a good run on speed 5 on the mixer for 3 minutes or knead it well on the table for 7 minutes until the dough is thoroughly kneaded. Cut the butter into small pieces and knead them into the dough; this takes a couple of minutes on a mixer. Cover the dough with a shower cap or cling film and let it rise for 60 minutes. After 60 minutes, turn the dough out onto a floured surface and divide it into 15-20 pieces. Make sure not to knock the air out of the dough, so be gentle. Shape the rolls and place them on 2 baking trays with parchment paper. There should be space between them so they can rise. Let the rolls rise again for about 30 minutes. In the meantime, preheat the oven to 240 degrees Celsius (464 degrees Fahrenheit) fan. Brush the rolls with beaten egg and put them in the oven one tray at a time. Turn the oven down to 210 degrees Celsius (410 degrees Fahrenheit) fan and bake the rolls for 10 minutes. Let the rolls cool on a wire rack afterward. Now you have the most delicious and fluffy birthday/tea rolls for coffee, cocoa, tea, or whatever you want to enjoy them with.