Finn's "Can we pleeeeeease have shepherd's pie for dinner?" Shepherd's Pie

Since Finn is my son and all, I never dated him but you might consider him the culmination of all the dating I did do. And Finn is an all meat and potatoes kind of guy. So I am posting his very favorite meal and putting his name in the title. And this isn't your grandma's shepherd's pie with green beans and canned tomato soup. Every time I make this I think, "I should take a picture of this so I can post it." But then by the time I actually get it on the table, I forget. So hopefully you can imagine flavorful ground beef mixed with vegetables, smothered in a light gravy and topped with lightly toasted, fluffy mashed potatoes.
Finn's "Can we pleeeeeease have shepherd's pie for dinner?" Shepherd's Pie.
5-6 medium potatoes, peeled and cubed
2 tbsp sour cream
1 large egg yolk
1/2 c cream or milk
1 tbsp olive oil
1 lb ground beef
1 carrot peeled and chopped
1 onion chopped
1/2 c frozen peas
2 tbsp butter
2 tbsp flour
1 c beef stock
2 tsp A-1 sauce
1 tsp sweet paprika
Boil potatoes in salted water until tender, about 12 minutes. Drain potatoes and add sour cream , egg yolk and cream. Mash potatoes until smooth. While potatoes are boiling, preheat skilet over medium high heat. Add 1 tbsp olive oil and then add ground beef. Season meat with salt and pepper. Brown and crumble meat for 3-4 minutes. Add chopped carrot and onion to the meat. Cook veggies with meat for 5 minutes, stirring frequently. In a small saucepan over medium high heat, melt butter and then add flour. Cook together for 2 minutes. Whisk in beef broth and A-1 sauce. Thicken gravy for 1 minute. Add gravy to meat and vegetables, then add frozen peas. Preheat broiler to high. Put meat mixture in a smaller casserole dish. Spoon potatoes over meat evenly. Top potatoes with paprika and broil 6 to 8 inches from the heat until potatoes are evenly browned.
Also we like ours with a little ketchup on top.