Heat milk and half the maple syrup in a saucepan until warm but not boiling.
Whisk egg yolks with cornstarch and salt in a separate bowl until smooth.
Slowly pour half the warm milk into yolks, whisking constantly to temper.
Pour egg mixture back into saucepan with remaining milk; cook, stirring constantly, until thickened.
Stir in butter and vanilla extract until fully combined.
Transfer pudding to bowls, cover with plastic wrap touching the surface, and refrigerate for at least 2 hours.
Top with whipped cream or nuts before serving.