Preheat oven to 225 degrees Celsius (435 Fahrenheit).
In a flat bottomed oven safe fry pan, melt the 125 grams (2 oz) of butter over medium heat.
Add the sugars and turn the heat up to high.
Allow the sugar to slightly caramelize (approx 5 minutes) and remove from the heat.
Carefully lay the apple rings into the caramelized sugar and continue laying apple rings atop one another until the pan or dish is full.
Replace the pan to the stove top and cook gently over medium heat for approximately 15 minutes, keep an eye on it as the apples can quickly burn.
While it cooks defrost the puff pastry and cut it into the largest circle possible
Remove the pan from the heat and allow it to cool slightly.
Once the apples have cooled, cover them with the puff pastry and tuck in the edges.
Melt the remaining butter and brush the pastry with it.
Bake in the oven for 15-20 minutes or until the crust is golden.
Remove and allow to cool slightly.
Gently run a paring knife around the edge of the tart to separate any stuck bits.
Place a large plate or serving platter on top of the tart and carefully invert and turn the tart out onto the platter.