Melt the butter in a large saute pan over medium-high heat. Once melted and foamy, add the onion, garlic, and red pepper flakes and saute until tender, about 2 to 3 minutes. Season with salt and pepper. Add the heavy cream and let thicken, stirring for just 1 minute.
Add the peas and the mint and cook until the peas are bright green and warmed through, another 5 minutes.