Pour milk into small saucepan.
Scrape in the seeds from vanilla bean; add bean.
Bring to a simmer. Remove from heat.
Meanwhile, in a medium bowl, whisk together egg yolks, sugar, cornstarch and almond extract.
Gradually and slowly, whisk hot milk mixture into yolk mixture. Return the mixture to the saucepan.
Whisk over medium heat until custard thickens and boils, about 2 minutes.
Discard vanilla bean.
Transfer custard to a bowl and place plastic wrap directly onto surface of custard; cover and refrigerate until cold, about 4 hours. ** see note
Preheat oven to 350°F.
Combined powdered sugar, butter, egg and salt in a small bowl.
Add in almond slices and mix to combine well.
Add this mixture to the cooled custard and mix until well combined.
Pour into chilled crust; smooth top.
Arrange apricot halves, round side up, on top of the filling.
Sprinkle with sliced almonds.
Bake tart until filling is set and golden, about 45 minutes ***see note.
Remove from oven.
Brush with honey or agave and return to the oven for 3 minutes.
Cool tart completely in pan.
Serve chilled or at room temperature.