Add egg, sugar, sourdough starter, flour, and buttermilk to a large bowl in the order listed. Mix thoroughly before adding baking soda; batter will be light and bubbly. Do not mix again.

Heat a lightly greased griddle over medium-high heat.

Drop batter by large spoonfuls onto the preheated griddle; cook until bubbles appear and the edges are slightly dry, 3 to 4 minutes. Flip and cook until pancakes sound hollow when tapped with a spatula, 2 to 3 minutes. Repeat with remaining batter.