In a large bowl, sift together the cake flour, baking powder, baking soda, and salt until well blended. In a stand mixer, mix the sugar, vanilla, shortening, and melted butter until fluffy and creamy; this should take about 2-3 minutes. Gradually add the egg yolks one at a time, mixing well after each addition, and then pour in the buttermilk.

Gently fold the dry mixture into the wet ingredients, stirring until just combined. Be careful not to overmix! Once combined, scrape down the bowl and cover the dough. Refrigerate for 30-60 minutes.

Lightly flour your work surface and roll out the chilled dough to about 1/2 inch thickness. Using a knife or pizza cutter, cut the dough into bars approximately 3½” by 1½”. Score the tops lightly to help them fry evenly.

In a deep pot, heat shortening to 350°F. Carefully drop in the dough bars, frying for about 2-3 minutes on each side or until golden brown. Remove them and drain on paper towels.

In a bowl, whisk together the confectioner’s sugar, vanilla extract, and hot water until smooth and glossy. Once the doughnuts have cooled slightly, dip the tops into the glaze, allowing the excess to drip off before placing them on a wire rack to set.