Brush dirt off porcini mushrooms with a clean cloth or vegetable brush. Slice into bite-sized pieces.
Pour beef stock into a saucepan over low heat. Cover and keep warm.
Heat 2 tablespoons olive oil in a skillet over medium heat. Cook garlic until lightly golden, about 1 minute. Stir in mushrooms; cook until slightly softened, 2 to 3 minutes. Pour in 1/2 cup wine; cook until alcohol evaporates, 3 to 5 minutes. Continue cooking until mushrooms are tender but still firm, adding a little beef stock if they look dry, about 10 minutes.
Remove skillet from heat; sprinkle half the parsley over mushrooms. Season with salt. Cover and keep warm.
Heat remaining 2 tablespoons olive oil in a stovetop pressure cooker. Cook spring onion until softened, about 1 minute. Add Arborio rice; cook and stir until toasted and coated with oil, 2 to 3 minutes. Increase heat and pour in remaining 1/2 cup wine; simmer until alcohol has evaporated and rice has absorbed most of the wine, about 2 minutes.
Stir beef stock into the pressure cooker. Seal according to manufacturer's instructions. Increase heat to high; cook until cooker whistles, about 5 minutes. Reduce heat to low and cook for 4 minutes.
Remove cooker from heat and release pressure according to manufacturer's instructions. Remove the lid. Fold mushroom mixture, with 1 to 2 tablespoons cooking liquid, into the rice. Stir in Parmesan cheese and butter. Let stand for 2 to 3 minutes. Sprinkle remaining parsley on top.
