In a bowl with a hand mixer, or in the bowl if a stand mixer fitted with a paddle, whisk together your dry ingredients; flour, brown sugar, and salt.
Add in your vanilla and room temp butter, mix well. Mixture should have a crumbly texture, add more flour if needed.
In a standard 9 ½” tart pan, dump your crust and using your hands or the back of a spoon, pack the crust into the pan firmly and evenly.
Set aside to be filled.
Add the golden syrup, heavy whipping cream, breadcrumbs, lemon zest, lemon juice, and egg to a medium saucepan.
Bring to a gentle boil on medium-high heat, stirring constantly.
Once a gentle boil has been reached, reduce heat and cook for 2 minutes, then remove from heat.
Pour mixture into your shortbread crust and place into your oven, preheated to 375℉.
Bake for 25-30 minutes until your filling has nicely browned, the crust should be a golden color.
Treacle tarts are typically served warm with whipped cream.
