In a small bowl, mix warm water with yeast and a pinch of sugar. Let sit for 5 minutes until frothy.
Warm the buttermilk until it feels slightly warm to the touch but not hot.
In a large bowl, whisk together flour, sugar, and salt. Make a well in the center.
Pour the yeast mixture, warmed buttermilk, and eggs into the flour well. Stir until a rough dough forms.
Add softened butter one tablespoon at a time, kneading after each addition, until the dough is smooth and elastic.
Cover the dough and allow it to rise in a warm place for about 60 minutes or until doubled in size.
Preheat the oven to 375°F (190°C).
Divide the risen dough into 8 equal portions and shape each into a round bun.
Place buns on a baking sheet lined with parchment paper. Lightly brush with buttermilk and sprinkle poppyseeds on top.
Bake buns for 20 to 25 minutes or until golden brown and cooked through.
Allow the buns to cool on a wire rack for 10-15 minutes before serving.