Set out the butter to come to room temperature.
Preheat the oven to 425 degrees. Peel the carrots and cut in half lengthwise and crosswise. If the carrots are big at the top, cut these pieces in half again lengthwise so all pieces are about the same size. Toss the carrots with the olive oil, thyme, salt and pepper. Roast in the oven for 25 minutes.
While the carrots are roasting, use a fork to mash the butter. Add the ground cumin, ground coriander and ground turmeric to the butter and combine.
When the carrots are done, remove them from the baking sheet with a spatula and place in a bowl. Add the butter and spices to the bowl. Stir to melt the butter then serve.