From the Saltie cookbook - this is an amazing lunch place in Williamsburg, Brooklyn, that does delightful salads and sandwiches, and, as it turns out, also amazing sweets.

1.25 tsp dried lavender flowers (or 2.5 tsp fresh)
225 g butter 
3/4 C granulated sugar
1 egg yolk
1 tsp vanilla extract
2 C flour
1/2 tsp salt
large granulated sugar, to sprinkle

Grind up the lavender flowers (mortar/pestle; spice grinder)
Cream butter and sugar until fluffy, add egg yolk and vanilla and beat until smooth.
Whisk flour, salt and lavender together, then add to the creamed mixture and beat till incorporated.
Flatten the dough, and if you have time, wrap in clingfilm and refrigerate for up to 1 week or overnight (unless you're like me, and you bake it instantly).
Preheat oven to 160C.
Grease a 10 inch (25cm) baking dish and line. Press in the dough, prick with a fork, and then sprinkle with sugar (and extra lavender if you wish). Bake approx 20 minutes, until golden brown.
Let cool till slightly warm, then cut into squares.