Preheat oven to 300*.
Place ramekins (like these ones) in a rimmed baking dish or casserole dish big enough for all of them to fit--2-9x13's works perfectly. Warm the cream on the stove over medium heat until hot in a medium saucepan; do not boil. While the cream is warming mix egg yolks, maple syrup, and salt together in a medium heatproof bowl--no plastic.
When the cream is hot add 1/2 cup of it to the egg mixture and whisk while pouring. Add another 1/2 cup and do the same. Add the rest of the cream to the bowl slowly and mix well. (You're "tempering" the mixture by not adding it all at once, this keeps it a good consistency and prevents the eggs from cooking.)
Mix in the vanilla and butter.
Using a ladle, pour the mixture into ramekins. It'll fill the 6 bowls almost to the top. Top with a sprinkle of nutmeg.
Carefully pour enough hot water into the rimmed baking dish to come halfway up the sides of the ramekins (don't get water inside them). A teapot is the easiest way to do this.
Bake until the edges are set but the center jiggles slightly, 45-50 minutes. Shut the oven off and let cool a few minutes. Carefully remove the ramekins from the water bath onto a dish towel and cool to room temperature.
You can either eat at room temperature or cover and refrigerate until chilled; however I think cold is best because it's still kind of runny just out of the oven, but sets up nicely when chilled.
I like to make this ahead of time for easy serving later. Add the berries & whipped cream just before serving.