lightly butter a 9“ x 13” glass baking
melt butter in pot over medium-low
when melted add the brown sugar and corn syrup and stir to combine
add sweetened condensed milk stir to combine
raise heat to medium and bring to a boil for 10 to 12 minutes
heat to a temp of 242 F
remove from heat, add vanilla and stir to combine
pour into glass dish
let cool and cover when room temp