MAKE THE LANCASHIRE BISCUIT DOUGH:
In a food processor, pulse flour, sugar, and salt to combine.
Add cold butter cubes and pulse until mixture resembles coarse breadcrumbs.
Add egg yolk, vanilla extract, and 2 tablespoons cold milk.
Pulse just until dough begins to come together, adding more milk if needed.
Turn out onto work surface and gently press into a cohesive dough (don't overwork).
Divide dough in half. Press each half into a rectangle, wrap in plastic, and refrigerate 30 minutes.

ROLL AND CUT THE BISCUITS:
Preheat oven to 350°F. Line two baking sheets with parchment paper.
On a lightly floured surface, roll out one portion of dough to 1/4-inch thickness.
Using a ruler and sharp knife or pizza cutter, cut into uniform rectangular bars (approximately 3x1 inches). Precision is key - the bars should look almost identical.
Transfer bars to prepared baking sheets, spacing them 1 inch apart.
Repeat with second portion of dough.
Refrigerate biscuits for 15 minutes before baking (helps maintain shape).

BAKE THE BISCUITS:
Prick each biscuit several times with a fork to prevent puffing.
Bake for 12-15 minutes until edges are lightly golden. The biscuit should be nice and crumbly and crisp.
Let cool on baking sheets for 5 minutes, then transfer to wire racks to cool completely.

MAKE THE CHOCOLATE AND ORANGE GANACHE:
Place chopped chocolate in a heatproof bowl.
In a small saucepan, heat heavy cream and orange zest until just simmering (do not boil).
Remove from heat and let steep for 5 minutes to infuse orange flavor.
Strain cream to remove zest (or leave it in for more texture and flavor).
Pour hot cream over chocolate and let sit for 1 minute.
Stir gently from the center outward until smooth and glossy.
Stir in orange liqueur or extract, butter, and salt until completely incorporated. The chocolate and orange ganache should be delicious.
Let ganache cool to spreadable consistency, about 20-30 minutes at room temperature.

ASSEMBLE THE TOSSET BARS:
Once biscuits are completely cool, spread or pipe ganache on half of the biscuits.
Use about 1-2 tablespoons ganache per biscuit, spreading evenly.
Top each with a second biscuit to create sandwich bars.
For a neater finish, you can dip the entire assembled bar in tempered chocolate, but the simple sandwich style is traditional.
If desired, garnish tops with a small strip of candied orange peel or a sprinkle of fresh orange zest.

SET AND SERVE:
Place assembled bars on a parchment-lined tray and refrigerate for 1 hour to set the ganache.
Store in an airtight container in the refrigerator until ready to serve.
Bring to room temperature before serving for best texture.