In a large measuring cup with a pour spout (mine is a 5 cup measuring cup) combine flour, sugar, baking powder, and salt until combined.
Create a well in the middle of your dry ingredients and add the milk, sourdough starter, eggs, and vanilla.
Using a fork or whisk begin to mix the wet ingredients in the center of the batter, gradually mixing the dry ingredients into the wet ingredients.
Mix until completely combined taking care to scrape the bottom of the measuring cup.
Fill a medium sized, heavy-bottomed pan with 2-3" of lard (or frying oil of your choice) and heat over medium heat until slightly smoking or shimmering. (A thermometer would read about 375°) - See notes for further information.
When the oil is preheated, pour a slow, thin stream of batter over the hot oil using a criss-crossing motion, creating the web of your funnel cake.
Fry for about 90 seconds before flipping using tongs or a wire spider. Fry another 60-90 seconds on the second side, or until golden brown.
Remove to a plate lined with a paper towel and immediately dust with powdered sugar and (optional) cinnamon.
Repeat the cooking instructions with the remaining batter, but allow the oil to reheat for a few seconds between batches to ensure even cooking.