In a bowl, whisk the flour, yeast and salt. In a small saucepan, heat the milk with the sugar until warmed, about 85°. Make a well in the center of the dry ingredients and pour in the warm milk. Stir until the dough is evenly moistened; it will be a little stiff. Cover and let stand in a draft-free area until billowy, about 2 hours.
In a small bowl, stir the baking soda into the warm water until dissolved. Using a handheld mixer at low speed, beat the liquid into the dough until smooth. Let the batter rest for 30 minutes.
Preheat a cast-iron griddle or large nonstick pan over moderate heat. Brush the pan with butter. If it browns right away, turn the heat down. Working in batches, brush the insides of 2 1/2-inch shallow ring molds with butter and set them on the griddle. Spoon 2 1/2 tablespoons of the batter into each ring, allowing it to flow to the edges. Cook over moderate heat for about 5 minutes, until the bottoms are golden and bubbles appear on the surface. Brush the tops with butter and invert the molded crumpets. Cook until golden on the bottom, about 2 minutes longer. Transfer the crumpets to a rack and carefully remove the rings. Repeat with the remaining butter and batter.
Serve the crumpets right away or slice and toast them. Serve with softened butter and Apricot-Praline Butter.
The crumpets can be refrigerated in an airtight container for up to 5 days.