Par-bake the tart and set it aside while you prepare the filling. If you want to see step-by-step photos on how to make the crust check out my post on how to make sweet shortcrust pastry.
Layer in the pear slices to slightly overlap. Then pour the custard mixture on top, make sure to pour evenly, and any pears that are sticky up gently press them to wet them into the custard mixture.
Bake for 30-37 minutes, the custard should be set and barely wiggle in the middle two inches or so. Let cool on a wire rack for two hours then wrap in plastic wrap and chill in the fridge for two hours.