Recipe(tried): here's a good one.

Cut the carrots into large-ish chunks and par-boil. Melt some butter in a pan, only about 1 or 2 teaspoons, add 1/2 tsp brown sugar and a teaspoon of cinnamon. Make sure all this melts together on a low heat. Add the carrot pieces and stir well to coat. If you;re going to freeze this then freeze at this point. To eat straight away just put a lid on and cook very gently until the carrots are soft.

To re-cook.

Defrost at room temperature, wrap in foil and bake in oven for about 30 minutes on a medium heat until the carrots are soft. The frozen butter will melt and baste the carrots.