Place the starter in a medium-sized bowl. Stir in the sugar and salt, then the baking soda. The batter should rise up and bubble a bit, becoming almost billowy.
Heat your griddle over medium-low heat; 300°F is perfect. Lightly grease the surface with cooking oil (if your pan isn't non-stick), then melt a pat of butter atop the oil.
Lightly grease four English muffin rings (4" across) and place on the griddle. Divide the batter evenly among the rings. Each ring will take a generous 1/4 cup of batter; a generously heaped muffin scoop is the perfect tool for this task. Cook for about 5 minutes, until the tops are set and full of small holes. Carefully flip the crumpets over, remove the rings (they should pop right off), and continue to cook for about 3 minutes, until they're golden on the bottom. Enjoy the crumpets warm, split and spread with butter and jam. Or toast to brown and crisp them before serving.