Add the milk, Greek yogurt, eggs, protein powder, sweetener, and vanilla into a large mixing bowl. Begin whisking slowly, then continue until the mixture becomes completely smooth, creamy, and fully combined. Make sure there are no lumps from the protein powder or yogurt, as this ensures a silky custard texture.

Once the mixture is ready, carefully pour it evenly into ramekins or a baking dish. Fill each one gently and avoid overfilling, leaving a little space at the top to prevent spilling during baking.

Place the filled ramekins into a deep baking tray. Slowly pour hot water into the tray until it reaches about halfway up the sides of the ramekins. This water bath helps the custard cook gently and evenly, preventing it from curdling or cracking.

Transfer the tray carefully into a preheated oven set at 160°C (320°F). Bake for 35–40 minutes, or until the custard is mostly set around the edges but still has a slight jiggle in the center when gently shaken.

Remove the tray from the oven and carefully take the ramekins out of the hot water. Place them on a flat surface and allow them to cool completely at room temperature. This step helps the custard finish setting gradually.

Once cooled, transfer the ramekins into the refrigerator and let them chill for at least a few hours. This chilling time improves the texture, making the custard firmer, smoother, and more flavorful.

When ready to serve, enjoy the custard chilled straight from the fridge, or let it sit at room temperature for a few minutes if you prefer a slightly softer, creamier texture.