Pre-heat the oven to 200C (180C fan forced).
Place the fry pan top down onto the pastry sheet and cut a circle just ever so slightly larger than the top of the fry pan.
Put the pastry circle aside whilst you assemble the filling.
Place the beetroot cut side down in the bottom of the fry pan. Squeeze them in and juggle them around until they fit.
Drizzle the vincotto over the beetroot.
Season the beetroot with salt & pepper.
Drape the caramelised onions over the beetroot.
Place the pastry circle over the top of the fry pan and tuck the pastry into the sides of the beetroot, as if you were tucking in a bed sheet.
Place the fry pan in the oven and cook for 30 minutes, or until the pastry is golden and well risen.
Remove from the oven and allow to sit for 5 minutes.
Place a plate over the top of the fry pan, and then flip the fry pan over.
Hold your breath and remove the frypan. Hopefully all of the pieces of beetroot have fallen into place in the pastry. If not, just place any stray beetroot pieces back in the holes.
Scatter over the crumbled feta and serve.