Whisk the egg yolks and cornstarch together in a bowl. In a medium saucepan combine the coconut milk, half-and-half, sugar, vanilla bean if using (if using extract or paste do not add yet), and salt and whisk together. Whisking occasionally, bring the cream mixture to a simmer (you should see tiny bubbles around the edges). When it begins boiling, pour (VERY SLOW AND IN A STEADY STREAM) about ½ cup of the cream mixture, while whisking the entire time, into the egg yolk and cornstarch mixture. Don't stop whisking or I promise you that you'll end up with scrambled egg yolks. Then in a slow stream, pour the egg yolk mixture into the pot while continuing to whisk and keep over medium/low heat.
Rather quickly, the custard will bubble and thicken. Keep whisking. Whisk and cook for 1 minute or so while it is bubbling . Remove from heat and stir in the unsweetened coconut, butter, vanilla, and coconut extract (if using).
Pour warm filling into cooled pie crust. Cover tightly with plastic wrap directly on the surface of the pudding (to prevent a skin from forminand refrigerate for at least 3 hours or overnight until chilled and thickened. Pie may be refrigerated for up to 1 day.
To make the meringue, fill a wide saucepan with water about ⅓ of the way. In a large stainless steel bowl of a stand mixer, put egg whites, sugar, salt and cream of tartar. Place the bowl over the simmering saucepan of water. Being whisking the egg white mixture and using a rubber spatula, scrape down the sides of the bowl. Do this until egg white mixture reaches 160 on a candy thermometer, about 12 minutes give or take. If you don't have a thermometer - don't worry, test the egg whites with you finger after about 10 minutes, if it is hot - but not so hot that you have to pull your finger back - then it is ready. If it is just warm, continue for another 2-3 minutes. Take the bowl off the sauce pan and attach to the stand mixer and using the whisk attachment, whip on high for about 8 minutes until the meringue is a light and fluffy ball.
To assemble the pie - take out your chilled pie and top with the meringue all the way to the crust (end to end to prevent the meringue from shrinking). Using an offset spatula, pillow the meringue into multiple small peeks.