In a large bowl, mix together the sugar, sour cream, lard, eggs, salt, baking soda, flour, and vanilla extract until a soft dough forms.
Turn the dough out onto a lightly floured surface and knead for 8-10 minutes.
Roll out the dough with a rolling pin until it is ½ inch thick, then cut into desired shapes using a donut cutter or cookie cutter.
Heat 3 inches of oil in a deep pot over medium heat. Once the oil reaches 350 degrees Fahrenheit, carefully place the donuts in batches into the oil. Fry for 2-3 minutes on each side until golden brown.
Remove the donuts from the oil with a slotted spoon and place them onto paper towels to drain and cool.
To make the glaze, in a medium bowl whisk together water, vanilla extract, and confectioners’ sugar until the mixture is smooth.
Dip each cooled donut into the glaze and place it on a wire rack to cool and harden.
Enjoy your freshly made Round Rock Donuts!