Melt the butter and lard or shortening into boiling water. Slowly add the flour and dough salt until a soft, nonsticky dough forms. Cover and chill for 45 to 60 minutes.
Sauté the diced onion in 1 tablespoon of the filling butter until softened and lightly caramelized. Cool briefly.
Combine the onion with the diced potatoes, carrots, stew meat, parsley, thyme, salt, and pepper. Preheat the oven to 350°F.
Divide the dough into 8 balls. Roll each into a 9-inch circle about 1/4 inch thick. Place about 1 1/2 cups filling on one side, dot with 1/2 tablespoon butter, moisten the edge, fold into a half-moon, and seal.
Arrange the pasties on a greased or parchment-lined baking sheet. Cut vents in the tops and bake for 30 minutes.
Brush the pasties with cream, return them to the oven, and bake about 30 minutes more, until the filling reaches 165°F and the vegetables are tender. Serve hot.