Mix the milk and egg yolks at a low speed in a heatproof bowl until the mixture is smooth.After adding the lime juice, whip the mixture for a little more.
Place the mixing bowl containing the custard on top of a big pot of simmering water. Stir until the custard thickens and thermometer reaches between 165 and 170 degrees F. Make sure the mixing bowl's bottom is not in contact with the boiling water.Pour the custard into the pie crust after straining it. Be aware that a genuine Key Lime pie is not green in hue.
Place it in the refrigerator to set for 6 hours or until firm, but best if overnight, after allowing it to cool for 20 minutes at room temperature.Get the whipped cream ready. Pour the cream and sugar into a refrigerated mixing bowl and whisk until the cream forms stiff peaks.On the pie's top, apply the whipped cream.