Step 1 Spoon yoghurt into a fine sieve set over a medium bowl; cover and refrigerate overnight to make labne. Discard strained liquid.
Step 2 Preheat oven to 160°C. Line a 2.5cm-deep, rectangular (11.5cm x 34cm) loose-based tart tin with pastry sheets, trimming to fit. Put tin in freezer for 20 minutes, or until pastry is frozen.
Step 3 Place tart tin on a baking tray and bake for 20 minutes, or until pastry is light golden. Transfer tin to a wire rack, leaving pastry to cool completely.
Step 4 Meanwhile, place labne in a large bowl; whisk in eggs, honey and orange zest until combined. Spoon mixture into cool pastry case and bake for 35–40 minutes, or until filling is just set and light golden. Leave tart to cool, then refrigerate until chilled.
Step 5 Arrange orange slices on top of tart, slice evenly and serve.