Step 1In a large mixing bowl, combine the flour, cornstarch, salt, sugar and baking powder. Pour in the buttermilk, then the beer. Gently fold using a spatula, careful not to whisk (a whisk will introduce too much air into the dough, which will make the beignets tough).
Step 2Set the batter aside for at least an hour to give the liquids time to mix and react for the fluffiest beignets. Then refrigerate the batter for 30 minutes before frying (when chilled, the beignets come out more airy and less dense).
Step 3Bring a pot of cooking oil to 350 degrees over medium-high heat. Use an ice cream scoop to portion the dough, dipping each portion in the oil. Fry until the dough is a light golden brown 4 ½ to 5 minutes. To make sure the beignets are cooked through, stick them with a long skewer. If the beignets are ready, the skewer will come out clean; if not, continue to fry.
Step 4Remove the beignets and drain before serving.