Melt the butter in a small saucepan over medium-low heat. Once melted, add the sugar, salt and heavy cream and cook until the sugar has melted, stirring with a rubber spatula.
½ stick unsalted butter, ¾ cup dark brown sugar, ½ cup heavy cream, ½ teaspoon kosher salt
Let it come to a simmer, then put a timer on for 3 minutes, without any stirring at all! If you stir it during this time it might become grainy.
Take it off the heat and add your whiskey (if using!) and vanilla extract, stirring briefly to incorporate. Pour into a large jar and let it cool completely.
1 tablespoon dark liquor, ½ tablespoon vanilla extract
Make Cake
Preheat the oven to 350°Fahrenheit/175°Celsius. Grease and line an 8×8 cake pan with parchment paper.
In a large mixing bowl, whisk the sugar with the eggs for 1 minute until you see some bubbles on the surface. Whisk in your cooled butterscotch sauce.
1 cup light brown sugar, 2 large eggs, ½ cup butterscotch sauce
Add the yogurt, oil, vanilla extract and salt and whisk once more until smooth.
½ cup yogurt, ½ cup neutral oil, 2 teaspoons vanilla bean paste, ½ teaspoon kosher salt
Fold in your flour, baking powder, and baking soda and fold until smooth.
1 teaspoon baking powder, 1 ½ cups all purpose flour, ¼ teaspoon baking soda
Pour into your pan. Bake for 35-40 minutes, a toothpick inserted should come out clean. Let it cool in the pan for 20 minutes then remove it and let it cool completely on a wire rack.
Make Frosting
In your stand mixer with the paddle attachment, beat the butter and confectioners’ sugar on low speed until well combined. Turn the speed to high for 2-3 minutes until light and fluffy.
Add in the salt and butterscotch spread and beat again on medium speed for 2 minutes.
¼ teaspoon kosher salt, ¼ cup butterscotch sauce
Notes
I make sure that all of my ingredients are at room temperature before I start the recipe, so pull out all of the ingredients before you start baking.Butter: I use European style butter, like Kerry Gold, in my recipes. This will make your frosting much creamier and richer.Salt: If you don’t have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt.Yogurt: You can substitute the yogurt for buttermilk or sour cream. Neutral Oil: Use an unflavoured oil like rapeseed, canola oil or vegetable oil.Storage: Keep tightly wrapped in the fridge for up to 5 days. Let it come to room temperature before eating.