Preheat the oven to 400°F.

Grease a deep 10-inch quiche pan.

Roll out the pie crust and press into the pan.

Line the crust with parchment paper and pie weights.

Bake for 10-12 mins, until pastry is cooked but still light in color.

Heat the olive oil and butter in a large skillet on medium-low heat.

Cook the onions, stirring, until tender, light brown and beginning to caramelize.

Stir in the fresh thyme leaves.

Set the onion mixture aside.

Whisk the light cream and eggs in a large bowl and season.

Stir in the grated Parmesan or Cheddar cheese, or a combination of both.

Spread the caramelized onion mixture evenly in the baked crust.

Pour the egg and cream mixture on top of the onions.

Bake for 30 to 35 mins, until golden brown and set.

Serve the French Onion Tart warm or at room temperature.

Garnish with microgreens, if desired, for a final touch.