Line a baking sheet with parchment paper or a silicon baking mat. Set aside.

In a heavy-duty 4-quart saucepan, melt butter.

Add the sugar, maple syrup, water, vanilla, and sea salt.

While stirring constantly, bring the mixture just to a boil. Lower heat to medium.

Brush down sides of pan with a brush dipped in hot water to prevent the sugar from crystallizing on the pan sides.

Stop stirring and clip a candy thermometer to the pan.

Cook for about 20 minutes, keeping a close eye on the temperature. If the toffee starts to darken in certain places and not others, gently swirl the pan. This will prevent hot spots and burning.

Once the toffee has reached the hard crack stage (at sea level, 300°F), remove pan from heat.

Quickly stir in the pecans and pour out onto the prepared baking sheet. Do not scrape the pan. Gently press the top of the toffee with a silicone spatula to spread it into a thin, even layer.

Let cool completely for 2-3 hours, or preferably overnight before breaking into pieces.

Once cooled, break into pieces and transfer to an airtight container or package up to give as gifts.