Melt 1 cup sugar over medium heat until deep amber (do not stir, swirl pan)
Carefully add 1 cup boiling water, stir smooth, simmer 3–5 minutes, then cool
Reserve ½ cup burnt sugar syrup for cake and ½ cup for frosting
Heat oven to 350°F / 175°C and grease three 8-inch pans
Cream 1 cup softened butter and 2 cups sugar for 3–5 minutes
Add eggs one at a time to the butter mixture
Whisk together cake flour, baking powder, and salt
Alternate adding dry ingredients and milk into the batter
Mix in ½ cup burnt sugar syrup and 2 tsp vanilla
Bake for 25–30 minutes and cool completely
For traditional frosting: boil ½ cup butter, 1 cup brown sugar, ½ cup burnt sugar syrup, and ¼ cup evaporated milk for 2 minutes
Cool frosting until warm, then beat in powdered sugar, salt, and vanilla
Frost cake quickly before frosting sets
Optional: For penuche frosting, melt ¾ cup butter and boil brown sugar, cream, and salt
Beat penuche mixture into melted butter with powdered sugar and add remaining butter 1 tbsp at a time
Rest penuche frosting 10–30 minutes until spreadable
Fill and frost cake with traditional burnt sugar frosting
Optional: cover outside with penuche frosting and finish with rustic swoops and swirls
