Important! Use a wide pan for this paella. Ideally, 11 1/2-inches wide. If you don’t have a pan this large, or if you don’t want leftovers, use a 9 1/2-inch pan, and cut the recipe in half - 1 cup rice x 2.5 vegetable stock, 1/2 cup sofrito, etc.
Preheat oven to 300°F. Heat the olive oil in a large (11 1/2-inch skillet) over medium heat- if you don't have a skillet that large, use a 9 1/2-inch skillet and cut the recipe in half. Sauce the carrots, scallions (or spring onions), until translucent. Stir in the garlic, and let it cook a little longer. Add the rice, stir well, and cook until the grains are also translucent, a few minutes - be mindful to not allow the rice to burn. Stir in the sofrito. Add the paprika. Crush the saffron with your fingers, and add that as well.
Move the paella to the oven and bake for another 12 minutes. Remove, and if you want to try to get a bit more crust on the base of your paella, and you’re confident your paella won’t burn, return the paella to a burner for another minute or so. Remove from heat and allow it to rest for another few minutes. Top with anything else you like - olives, nuts, lemons, herbs, etc. Serve family style in the pan.
Recipe (especially the timing) inspired by the Arroz En Paella con Verduras de Primavera in Paella, by Alberto Herraiz (Phaidon 2011). Brindisa by Monika Linton (Fourth Estate, 2017) was also a good reference for this recipe related to the sofrito, etc.