I use this method with both steak and burgers and - although I do use gas - it doesn't involve tipping your pan so should work.
Sear the meat both sides in a hot pan (depending on thickness and how you want it cooked)
Sit a large knob of butter on top on the centre of meat
Put the whole pan in a warm oven (~100C) for around the same amount of time as the ...
You definitely can.
Use a thick, heavy cast iron skillet and you won't have any problems at all - lifting the skillet off the heat for a couple of seconds won't affect the cooking because of the skillet's thermal mass.
You have 2 options to remove varnish at home:
Mechanical removal by sanding or scraping by hand or using a rotary tool. If you are too aggressive with this you could damage the pan, but if it is done right you will get a lot off. This could be tricky because of the shape of the pan, all of the curves and few flat spots, hand sanding will probably give you ...
Le Creuset say 450°F/230°C is the maximum temperature their enamelled cast-ironware will take. Other manufacturers seem to be sometimes lower, though that could be a handle/lid requirement rather than the enamel itself - see Why are most enameled cast iron dutch oven's only rated up to 400-450 F?
Your problem, assuming you season the mortar with a low-...