Add butter, sugar and lemon zest - beat till fluffy. Add lemon juice and egg yolk - mix to combine.

Add flour, cornstarch and salt fold till combined. Divide dough into 2. Set each piece onto parchment or cling wrap. fold over and roll into a cylinder about 1-1/2 inches. Chill dough at least 2 hours. When ready to bake heat oven to 350 deg F. Slice to 1/4 inch.

Bake for 12 to 17 mins rotating pans. Golden around edges. Dust with sugar. Store at room temp in an air tight container.