In a large bowl, whisk together flour, rolled oats, salt and bicarb soda. Stir in the raw sugar and brown sugar and mix until smooth.
Stir vanilla into melted butter and pour mixture over dry ingredients. Stir mixture until well combined. Pop half of the crumb mixture into the bottom of a greased slice tin and press into an even layer. Bake in preheated oven for 15 minutes.
Remove from oven and put aside (leave the oven turned on). In a bowl, whisk together sweetened condensed milk, lemon zest, lemon juice, egg yolks and lemon extract until well blended.
Pour mixture over crumb crust in baking dish and spread into an even layer. Sprinkle the remaining crumble mixture over the top of the lemon layer. Bake in oven for 23 - 26 minutes or until lightly golden.
Remove from oven and allow to cool. Cover and refrigerate for at least 1 hour then cut into squares. Store in airtight container in refrigerator.
OMG this is divine. Really easy to make and who says you have to wait for it to cool!! We did, only just, manage to get some of it into the fridge. Used light condensed milk and didn't have any lemon essence on hand so put more lemon juice and zest in. Halved the sugar too - worked well. - 09 Jun 2014
This was lovely either cold or warmed up slightly under the grill ... Next time i make it i will do the topping as a normal crumble rather than the same as the base, that would be even yummier ! - 04 Jun 2015