Heat the olive oil and butter in a large skillet over medium heat. Once melted, add the chopped onion and sauté for about 5 minutes until it's translucent. Next, throw in your diced carrots and broccoli florets. These veggies will help create a hearty filling. Keep cooking for another 7-8 minutes until the vegetables soften. It’s time for the brisket. Add the chopped smoked beef brisket to the skillet and stir everything together. Let it cook for another 5 minutes.

Sprinkle the flour over the mixture. The flour will help create a nice gravy. Stir it well, allowing it to coat the brisket and vegetables.  Pour in the beef stock and add Worcestershire sauce. This will enhance the savory notes. Cook on medium heat until the mixture thickens and bubbles gently. Remember to stir occasionally!

While the filling is thickening, put the quartered potatoes into a large pot and cover them with cold water. Add a pinch of salt for flavor. Bring the pot to a boil and then lower the heat to simmer for about 15-20 minutes, or until fork-tender. Drain the potatoes and return them to the pot. Add the sautéed garlic, butter, sour cream, and heavy cream or half-and-half. Use a potato masher to create a creamy consistency. Mix in the jalapeño, cheddar cheese, smoked paprika, and season with salt and pepper.

Preheat your oven to 400°F (200°C). Spread the brisket filling in a large baking dish. Then, gently spread the mashed potato mixture on top. Use a fork to create some texture—they'll develop a crunchy crust when baked.

Bake the dish in the preheated oven for about 25-30 minutes or until the topping becomes golden brown. Allow it to cool for a few minutes before serving.