Heat the oven to 350°F. Spread the pecans on a baking sheet and toast them for 6 to 8 minutes, then let them cool.

Set a heavy-bottomed saucepan over medium heat. Melt the butter with the brown sugar, then add 2 cups of the half-and-half. Cook for about 5 minutes, until the edges begin to bubble. Stir often so the sugar melts smoothly.

In a bowl, whisk the remaining 1/2 cup cold half-and-half with the cornstarch and egg yolks. Then whisk in about 1/4 cup of the hot mixture to temper the eggs.

Pour the egg mixture slowly back into the saucepan while whisking constantly.

Keep cooking over medium heat and whisking all the while until the filling starts to thicken. Then lower the heat and simmer for 1 to 2 minutes more, still whisking. The filling should look smooth, glossy, and pudding-like.

Take the pan off the heat and stir in the vanilla. Pour the filling into the baked pie shell and let it sit at room temperature for 5 minutes.

Press plastic wrap directly onto the surface and chill the pie until fully set, at least 4 hours or overnight.

Remove the plastic wrap. Spread the whipped topping over the chilled filling, then sprinkle on the toasted pecans and toffee bits.

Keep the pie chilled until serving, and refrigerate any leftovers, covered, for up to 3 days.