In a small bowl, mix together water, 1/2 teaspoon sugar, and yeast. Set aside.
In mixing bowl with the hook attachment, mix together flour, salt, and remaining sugar.
Lightly beat 1 egg with the yogurt. Add the egg mixture, yeast mixture, and butter and mix on speed 2-3 until dough no longer sticks to the sides and it forms a ball, about 3-4 minutes.
Cover the bowl with plastic wrap and leave to rise until double in size, about an hour or 2 depending on temperature of the room.
Cover two 9 by 13 inch pans with parchment paper. Divide dough into 10 equal pieces. Flatten each piece into a circle and gather the edges into the middle and flip over to form a ball. Place 5 on each pan, spacing evenly.
Spray plastic wrap with nonstick spray and cover the buns. Allow to rise another 30 minutes.
Fill a deep pan halfway with water and place on the bottom rack in the oven. Preheat the oven to 400 degrees.
Beat 1 egg with a splash of water. Brush each bun with egg wash and sprinkle with Everything Bagel seasoning, if desired.
Bake one pan at time at 400 degrees until buns are lightly brown, about 12-15 minutes.*
Let cool for about 5 minutes, then place buns on a cooling rack and allow to cool completely. Keep buns in an air-tight container.