Heat oven to 180C/160C fan/gas 4.
Pulse the flour, oats and butter in
a food processor until crumb-like,
add the grated carrot and continue
to process until the mixture comes
together to form a ball. Alternatively
rub the butter into the dry ingredients,
add the carrots and press together
until a ball is formed. Carefully roll
out the pastry and line a metal 25cm
pizza dish or shallow tart case. Chill.
Gently cook the onions in oil for
about 15-20 mins until beginning to
caramelise. Place the beetroot in
the pastry case and cover with the
onions. Whisk the eggs and milk
together, season and pour over the
onions and beetroot. Bake in the
oven, lowering to 160C/140C fan/
gas 3 after 15 mins, for 40 mins or
until firm and golden.