Combine yeast, sugar and water in the bowl of a stand mixer (or a large mixing bowl) and whisk together. Let it sit until the liquid is foamy.
Add 3 cups of flour and mix on low (or by hand) for about one minute. Add 2 Tbsp of soft butter, egg and salt and continue to mix on low speed until the ingredients are well combined.
Turn the mixer up to medium speed and add flour 2 Tbsp at a time, waiting 60 seconds before adding more, until the dough is smooth and elastic and pulls easily away from the sides of the bowl. (I used 3 ½ cups + 2 Tbsp of flour.) The dough is ready when you push your finger into it, it leaves a mark, and you can pull your finger out without dough sticking to you.
Cover the dough with a kitchen towel and place in a warm spot to rise until double in size, 1-2 hours.
Punch the dough down and turn it out onto a floured surface. Divide the dough into 16 equal pieces and place them 2 inches apart on a cookie sheet lined with a silpat mat.
Melt the remaining 1 Tbsp of butter and lightly brush the tops of the rolls. Cover gently with a towel and let it rise until doubled in size, 30 to 40 minutes.
Meanwhile, preheat the oven to 375F.
When the rolls have finished rising, bake for 12-15 minutes until golden brown on the outside (note that einkorn flour will darken more quickly than conventional all-purpose flour).
Best served immediately when warm. Keep leftover rolls in a container with a lid at room temperature for 3 days, or in the refrigerator for u to 5-7 days.