Don’t skip straining the custard! No matter how hard you try, sometimes the eggs will scramble a little. Straining double ensures that the custard is nice and smooth.
If you don’t want to buy superfine sugar, regular granulated sugar will work as well. It will just take longer to caramelize.
You can also caramelize the sugar under a broiler in the oven. Place the oven rack as close to the top of your oven as possible and broil for about 1-2 minutes, occasionally rotating the pan, until the sugar is evenly melted and browned. Don't over-do it, or the custard will warm up and melt!