For dough: In a small bowl, stir together ¾ cup warm water and yeast. Let stand for 5 minutes until foamy.
In the work bowl of a stand mixer fitted with the paddle attachment, stir together flour and next 3 ingredients. Add yeast mixture, buttermilk, butter, and eggs, and beat at low speed just until dough forms.
Switch to dough hook attachment, and continue beating on low speed for 5 to 7 minutes or until dough is smooth and elastic (dough should stick to bottom of bowl but not sides).
Spray a large bowl with nonstick cooking spray, and place dough in bowl, turning to grease top. Cover with plastic wrap, and let rise in a warm draft-free place (85˚) until doubled in size.
On a lightly floured surface, roll dough to ¼-inch thickness. Using a sharp knife, cut dough into triangles.
In a large Dutch oven, pour oil to a depth of 3 inches, and heat over medium heat until a deep-fry thermometer registers 350°.
Fry dough, in batches, for 2 to 3 minutes per side or until golden brown. Let drain on paper towels.
Meanwhile, for glaze: In a small bowl, whisk together confectioners’ sugar and buttermilk. Dip warm beignets into glaze, and sprinkle with sanding sugar. Serve immediately.
