Preheat your oven to 350°F (175°C). In a food processor, blend the Saltine crackers and milk chocolate toffee pieces until finely ground. Mix in melted butter and press firmly into a pie dish. Bake for 10-12 minutes until golden brown, then set aside to cool completely.

In a saucepan over medium heat, melt the unsalted butter and whisk in the dark brown sugar until blended. Gradually add the heavy cream, stirring constantly until thickened, approximately 5-7 minutes. Remove from heat; stir in salt and vanilla extract.

Whisk the egg yolks and cornstarch until smooth. Slowly add a cup of the hot butterscotch to the yolks while whisking to prevent scrambling. Return this mixture to the saucepan and cook over low heat for 3-5 minutes until thickened, stirring constantly.

Pour the butterscotch pudding into the cooled crust, smoothing it out. Cover with plastic wrap and refrigerate for at least 4 hours until firm.

In a chilled bowl, whip the heavy cream with granulated sugar until soft peaks form. Spread the whipped cream over the top of the chilled pie and optionally drizzle with reserved butterscotch and garnish with toffee bits or chocolate shavings.