Line an 8 inch square pan with parchment paper.
Spread unsalted butter over the surface of the parchment paper. Set aside.
Sprinkle a marble board with water.
In a 4 quart saucepan, combine sugar, milk, maple syrup, and corn syrup.
Place over medium low heat.
Cook and stir until sugar is completely dissolved, about 5-6 minutes.
Stop stirring.
Brush down sides of pan with a pastry brush dipped in water.
Allow to cook, without stirring,to 238℉.
Pour out onto marble surface. Do NOT scrape the pan.
Dot with butter.
Allow to cool to 110℉.
Use a bench knife to scoop candy into the bowl of a stand mixer fitted with flat beater attachment.
Add vanilla.
Beat on high speed until candy thickens and loses its gloss, about 10-12 minutes.
Immediately spoon into prepared pan.
Spread evenly.
Allow to cool completely before cutting.