Preheat the oven to 180C/350F and grease and line an 8x8 square pan. (I use Wilton Bake Easy spray and greaseproof paper.)

Place the sugar, flour, bicarb, oats and zest of 1 lemon into a large bowl and toss to combine.

Add in the vanilla extract and stir.

Add in the cubed butter and, either using a pastry blender, or your hands, rub in the butter until you have what resembles coarse breadcrumbs. A few larger lumps is fine.

Place 2 cups of mixture into the bottom of your greased pan and lightly press down until level.

Spread the 3/4 cup of jam over the base, leaving a 1/4 inch gap around the side.

Sprinkle the remainder of the crumbly oatmeal mix over the top of the jam, then lightly press to level.

Place in the oven for 35-45 minutes until lightly golden on top and the jam is bubbling.

Leave in the pan for at least an hour before trying to take them out. They will firm up as they cool.

Cooled bars will keep in an airtight container, at room temperature for 3 days.