Place 600 ml coconut milk, 2 TB raw sugar, and 2 ½ TB cornstarch in a saucepan and whisk thoroughly to blend.
Turn the heat on under the saucepan to a medium-high setting. Stir constantly with a spatula and scrape the bottom of the pan to prevent coconut milk from burning.
Bring to a full boil and reduce heat slightly. Continue cooking for 30 seconds or until the mixture has clearly thickened and is smooth.
Transfer the cooked mixture to a large measuring cup with a pour spout. Cover and let it cool for 5 minutes.
Uncover the coconut panna cotta and stir to blend. Pour it equally into 4 dishes.
Cover or wrap the dishes well and place them directly into the refrigerator. Chill for at least 4 hours or overnight.
Make mango sauce
Peel and slice the mangoes into attractive 2-inch slices. Measure out ¾ cup of sliced mango and process it in a small mixer or food processor with 2 TB raw sugar. You'll have a smooth spoonable sauce.
Unmold dessert
Place coconut panna cotta with its glass dish in a large bowl with about an inch around the sides. Carefully pour boiling water into the empty bowl.
Set a timer for 30-45 seconds. Remove the dish from the hot water bath.
Run a thin sharp knife around the top edge of the small dish no more than ¼ inch down the side. Place a flat serving plate over the top. Invert while holding the plate and dish firmly together.
Now the plate should be on the bottom with the molding dish upside down on top of it.
Jiggle the dish to coax the coconut panna cotta to drop out of it. You can tilt the dish up and slide the tip of a knife down the inside edge of the dish if needed to release the dessert.
Top with mango slices and coulis
Spoon a couple of tablespoons of mango sauce onto the plate with the coconut panna cotta and arrange mango slices along the side. Add a mint sprig or single strawberry to garnish the dessert if desired.
Store
This vegan panna cotta will keep 3 days in the refrigerator before the texture changes. Store the dessert in its molding dish separate from the mango slices and sauce. Plate the dessert just before serving.
Notes
Whisk coconut milk, sugar, and cornstarch together thoroughly before cooking.
Stir vegan panna constantly and scrape the bottom of the pan with a spatula while bringing it to a boil.
Unmold individual desserts by warming each dish's bottom in a hot water bowl. 30-45 seconds is sufficient. Avoid leaving the dish in the water too long, or the dessert may separate when the mold is removed.
Mango will make the prettiest slices if it's smooth, stringless, and not overly ripe.