Line an 8x8 baking dish with parchment paper. Set aside.
In a medium saucepan, add cubed butter, allulose, and salt. Heat over medium heat until melted.
Keep heating, stirring almost constantly, until mixture reaches about 260 degree on a candy thermometer, or turns rich and amber in color.
Remove from heat, stir in extracts. Wait 2 minutes, then por into baking dish evenly. Allow to cool 2 additional minutes.
Top with chips. Cover with foil. Allowing chips to melt.
Smooth top with spatula, sprinkle with nuts and optional additonal flaky sea salt.
Allow toffees to fully cool before refrigerating. Cut into 16 even squares.