In a large mixing bowl, combine the all-purpose flour, sugar, salt, and instant yeast. Whisk together until well blended.
In a separate bowl, whisk the room-temperature butter, large egg, and lukewarm water until combined. Gradually add the wet ingredients to the dry mixture, stirring until a dough begins to form.
Turn the dough out onto a floured surface and knead for about 8-10 minutes until it is smooth and elastic. If the dough is too sticky, sprinkle a little more flour as needed.
Place the kneaded dough in a lightly greased bowl and cover it with a kitchen towel. Allow it to rise in a warm place for about 1 hour or until it has doubled in size.
Once the dough has risen, punch it down to release any air. Divide the dough into 8 equal pieces and shape each piece into a smooth ball. Place the balls on a baking sheet lined with parchment paper, ensuring they are spaced apart.
Cover the shaped buns with the kitchen towel again and let them rise for another 30-45 minutes until they have puffed up.
While the buns are rising, preheat your oven to 375°F (190°C).
In a small bowl, whisk the egg white and brush it over the tops of the risen buns. Sprinkle poppy seeds generously on top.
Bake the buns in the preheated oven for 15-20 minutes or until they are golden brown. Remove from the oven and let cool on a wire rack before slicing.
