Start by gathering all your ingredients. Line a baking sheet with parchment paper and set aside.
In a dry skillet over medium heat, toast the sliced almonds for about 5-7 minutes, stirring frequently until golden and fragrant. Remove from heat and set aside.
In a heavy-bottomed saucepan, combine the unsalted butter, sugar, and water. Cook over medium heat, stirring until the sugar has dissolved.
Once the sugar is dissolved, stop stirring and allow the mixture to come to a boil. Clip a candy thermometer to the side of the pan. Continue boiling without stirring until the mixture reaches 300°F (hard crack stage).
Remove the toffee from heat and stir in the vanilla extract and half of the toasted almonds. Quickly pour the toffee onto the prepared baking sheet, spreading it out evenly.
Place the unwrapped milk chocolate bars on top of the hot toffee. Let them sit for a few minutes to melt, then spread the melted chocolate evenly over the surface.
Sprinkle the remaining toasted almonds over the chocolate layer and finish with a light sprinkle of coarse sea salt, if desired.
Allow the toffee to cool completely at room temperature. Once set, break it into pieces and enjoy your delicious Chocolate Toffee with Almonds!