Preheat the oven to 400°F (200°F). Line a baking sheet with a sheet of parchment paper.
Prepare the frangipane: To a medium bowl, add the almond meal/flour, sugar, butter, and almond extract. Mix everything together with a rubber spatula until combined. Add in the egg, then mix until incorporated well. Temporarily set aside.
Warm the jam in the microwave or a small saucepan until hot and runny. Use a pastry brush or a butter knife to spread the jam onto both sides of each brioche slice. Place the brioche slices onto your prepared baking sheet.
Use a spoon to scoop the frangipane onto the tops of each brioche slice, using the back of the spoon to spread a thick, even layer. Sprinkle the tops with shaved almonds.
Bake the bostock pastries for 12 to 15 minutes, until the franipagne has puffed up and the shaved almonds are beginning to golden. Before serving, dust with powdered sugar.
Mmmm I love handmade marzipan! It's funny though, because I thought I didn't like marzipan at all until I made it at home, and that's when I realised that it's just almond extract / flavouring that I hate. So I just don't put it in - I usually add grated orange peel instead