Begin by adding warm water, warm milk, yeast and sugar to stand mixer and stir or whisk together. Let sit for 5 minutes until the mixture becomes frothy.
While mixture above is sitting, beat 1 egg. Reserve second egg for end of recipe.
In large bowl whisk together flours (bread flour and all purpose flour) and salt. Once combined, add in soften butter and rub into flour using fingers until the flour mixture becomes crumby.
With the frothy water, milk, sugar and yeast mixture in the bowl, add in flour mixture and egg. Use dough hook to combine dough on low until the dough ball begins to form. Once formed, turn to medium speed and beat for 5 minutes.
After the five minutes, remove the bowl from the stand and cover with plastic wrap. Allow for dough to double in size for at least 1 hour.
Line a baking sheet with parchment paper. Remove dough from the bowl and cut into 8 equal pieces. Roll each piece of dough into a ball and place on sheet. Cover with kitchen towel and allow to double in size for at least 1 hour.
Preheat oven to 400°F and place a oven save dish in oven filled half way with water on the bottom rack.
When the buns have doubled in size, take towel off and brush on egg wash. Egg wash is one beaten egg and 1 TBS water. Top with poppy seeds.
Bake in 400°F for 15 minutes, turning pan halfway through the baking process.
Transfer buns to baking rack to allow to cool.
When ready to serve, cut in half and serve with sandwich. (Don’t cut each of them open if not using all. These may dry out sooner than you’d like.)