In a mixing bowl, combine the yeast and sugar then pour the warm water over the top. Set aside for 5 minutes to active the yeast (bubbles should form on the top).
Add in the flour, starting with 1 1/2 cups, and salt and mix by hand (you can also use a stand mixer for this). Knead 3-5 minutes. The dough should be soft and a bit sticky. In warmer weather, you might need more flour but don’t use more than 2 cups.
Set dough aside for 10 minutes.
Make filling: mix butter, parmesan, garlic, and parsley
Preheat oven to 400 degrees F. and line a baking sheet with parchment paper.
Roll out the dough on a lightly floured counter to 1/4 inch thick. Cut out circles with a cookie cutter or top of a drinking glass. Transfer circles to the parchment paper.
Fill each piece of dough with 1 tsp of the butter mixture, brush the edges with egg yolk, and pinch the corners to create a triangle.
Melt remaining filling and brush on the tops and edges of the dough.
Bake for 10-12 minutes, until the tops are golden brown and the filling is set. Eat up!