Preheat your oven to 160°C and take a large baking tray that will be used for the water bath. Place your ramekins or baking dish inside this tray so everything is ready before you start mixing. This setup is important because custard cooks gently, and the water bath helps prevent it from curdling or becoming rubbery.

In a clean mixing bowl, crack the eggs and add the sugar-free sweetener along with the vanilla extract. Using a whisk, gently mix everything together until the mixture becomes smooth and slightly pale in color. Avoid whisking too aggressively, as incorporating too much air can create bubbles that affect the final texture.

Slowly begin pouring in the milk while continuing to whisk gently. Add it in a steady stream rather than all at once, making sure it blends smoothly with the egg mixture. Keep the motion slow and controlled so the mixture stays silky without becoming frothy.

Add the Greek yogurt and protein powder to the bowl. Whisk gently until everything is fully combined and the texture becomes smooth and creamy. Make sure there are no visible lumps from the protein powder, as these can affect the consistency of the custard once baked.

For an extra smooth and professional-quality custard, pour the mixture through a fine sieve into another bowl. This step removes any small lumps, foam, or egg strands, resulting in a perfectly silky texture after baking.

Carefully pour the prepared custard mixture evenly into the ramekins or baking dish. Try to pour slowly and steadily to avoid creating bubbles on the surface. If you notice any small bubbles, you can lightly tap the ramekins on the counter to release them.

Heat some water until it is hot (but not boiling), then carefully pour it into the outer baking tray. Fill it until the water reaches about halfway up the sides of the ramekins. This water bath ensures the custard cooks evenly and gently, preventing cracks and maintaining a creamy texture.

Carefully transfer the entire tray into the preheated oven. Bake for 35 to 40 minutes, keeping an eye on the texture toward the end. The custard is ready when the edges are set but the center still has a slight jiggle when gently shaken.

Once baked, remove the tray from the oven and carefully take the ramekins out of the hot water. Let them cool at room temperature for a while. This gradual cooling helps the custard set properly without becoming dense.

After the custards have cooled, transfer them to the refrigerator and chill for at least 2 to 3 hours. This step is essential for achieving the perfect creamy texture and allowing the flavors to fully develop before serving.