Heat a large skillet over medium-high heat and add the ground beef, breaking it apart with a spoon; cook for 5 to 7 minutes until deeply browned and no pink remains.

Add the finely diced onion and minced garlic to the skillet and sauté for 2 to 3 minutes until the onion is translucent and the garlic is fragrant.

Push the beef and aromatics to one side, add 4 tablespoons butter and let it melt; sprinkle 3 tablespoons flour over the mixture and stir constantly for 1 to 2 minutes until the flour turns light brown.

Slowly pour in 2 cups of whole milk while whisking constantly to prevent lumps, ensuring a smooth sauce.

Stir in 1 teaspoon salt, 1/2 teaspoon black pepper, 1/4 teaspoon garlic powder, 1/4 teaspoon onion powder, and 1/4 teaspoon cayenne pepper; mix well to distribute the seasonings.

Reduce the heat to medium and simmer the sauce for 3 to 4 minutes, stirring occasionally, until it thickens enough to coat the back of a spoon.

While the sauce simmers, toast the 8 slices of bread in a toaster or toaster oven until golden and crispy, about 2 to 3 minutes per side.

Remove the toast and immediately spread 2 tablespoons butter evenly across the hot slices so it melts into the bread.

Arrange the buttered toast on plates and generously spoon the creamed beef sauce over each slice; serve immediately while hot and the toast is still crispy.