In a large bowl, whisk together the flour, baking powder, and salt. Set aside.
In a medium bowl combine the warm water, warm milk, melted butter, sugar, and yeast. Whisk well to combine and completely dissolve the yeast.
Add the warm liquids into the large bowl with the dry ingredients and mix well (hand whisking or using a stand mixer with a whip) until the dough forms a sticky batter with lots of bubbles (about 7-9 minutes of vigorous hand whisking or 3-4 minutes of stand whisking at medium/high speed), scraping down the sides of the bowl as needed.
Cover the bowl with plastic wrap and allow the batter to proof (expand) for 1 hour in a warm spot in the kitchen.
Heat a griddle pan or crepe pan over medium/low heat. Spray the pan, and a ½ cup measuring cup with cooking spray (to make the sticky batter easier to work with). Place the silicone molds onto the griddle pan and spoon ½ cup of batter into each of the silicone molds, spreading the batter evenly with a knife or spoon if needed.
Cook the crumpets for approximately 5 minutes on the first side and then gently wiggle the silicone molds off. Set the molds aside. Use a spatula to carefully flip each crumpet and cook for an additional 4 - 5 minutes.
Remove the finished crumpets to a wire rack and continue the process with the remaining batter. Keep the crumpets warm in a low (200℉) oven until ready to serve.
Serve warm with butter and jam. These are also great toasted.