In a medium bowl, stir together the yeast, water, and 2 teaspoons of the sugar. Let the mixture stand until foamy, about 5 minutes.

In the bowl of a stand mixer fitted with a paddle attachment, combine the yeast mixture, milk, butter, eggs, salt, and remaining 1/2 cup of the sugar. Beat on medium-low speed until combined, 30 seconds.

Gradually add the flour, beating until completely combined, about 4 minutes.

Increase the mixer to medium speed and beat until a smooth and elastic dough forms, about 6 minutes.

Transfer the dough to a large bowl lightly greased with nonstick cooking spray. Cover tightly with plastic wrap and let stand in a warm place until doubled in volume, 45 minutes to 1 hour.

Deflate the dough, divide it into 2 pieces, and roll each into a rectangle. Add butter, sugar, and cinnamon for filling, then shape into rings.

Let the dough rings rest until doubled in volume, 30 to 45 minutes, then bake at 350°F for 22 to 28 minutes.

Let cool for 1 1/2 hours.

For the glaze, whisk together powdered sugar, milk, butter, and vanilla until smooth. Pour over cooled cakes and top with sparkling sugars.