Add the onion, green onions, garlic, Scotch bonnet, and thyme leaves to a food processor and process until almost a paste. Set aside.
Add the ground beef to a medium saucepan, sprinkle in the all-purpose seasoning, sugar, salt, allspice, and nutmeg, and stir until the raw beef is evenly coated. Stir in the processed vegetable mixture, then add the beef broth and ketchup and stir again.
Set the pan over medium-high heat and cook, stirring to break up any clumps, just until the mixture comes up to a simmer. Reduce the heat to medium and simmer, stirring occasionally, for about 20 minutes, until the beef is cooked through and the mixture is saucy but not watery.
Stir in the browning, then add the breadcrumbs and cook about 10 seconds, just until evenly distributed. The filling should be thick, moist, and hold together when scooped. Remove from the heat, taste and adjust salt if needed, then cool to room temperature and refrigerate until completely cold.
Make the bread and assemble
In the bowl of a stand mixer or a large mixing bowl, combine the flour, yeast, salt, and sugar and stir to blend. Pour in the water and coconut milk and stir until a shaggy dough forms, then add 2 tablespoons of the softened butter and mix until incorporated.
To knead with a stand mixer, switch to the dough hook and knead on low speed for 6 to 8 minutes, until the dough is smooth, elastic, and slightly sticky. To knead by hand, turn the dough out onto a lightly floured surface and knead for 8 to 10 minutes, until smooth, elastic, and slightly sticky.
Shape the dough into a ball and place in a lightly greased bowl, turning to coat. Cover and let rise in a warm spot until doubled in size, 1 to 2 hours.
Line a baking sheet with parchment paper. Turn the dough out onto a lightly floured surface, gently press out the air, and divide into 8 equal pieces. Shape each piece into a ball, then roll each one into a 7-inch circle.
Place about ¼ cup of cold beef filling on one half of each circle, leaving a clean border. Fold the empty half over the filling to form a half-moon and press the edges firmly to seal.
Arrange on the prepared baking sheet, cover loosely with plastic wrap or a clean kitchen towel, and let rise for about 20 minutes, until slightly puffed.
Bake for 18 to 20 minutes, until lightly golden on top and lightly browned on the bottom. Remove from the oven and, while still hot, rub the tops with the remaining 2 tablespoons softened butter. Let cool slightly before serving warm.
Notes
Make ahead: The filling can be made a day ahead and refrigerated until cold and firm enough to portion. Storage: Refrigerate leftover meatloaves in an airtight container for up to 3 days. Reheat in a 350°F (175°C) oven until warmed through.