Lemon Thyme Substitute In the following recipe, lemon thyme is used. Unfortunately, I can't find it in my local grocery store. 

1) Can I substitute thyme + lemon zest? If so, how much?

2) The recipe notes rosemary and lavender both work and these are significantly easier to find. If I wanted to use these, how much would I use? 

I'd be interested in knowing the answer for dried and fresh herb substitutes.

Despite the recipe using metric measurements and spelling, I am American, so if this stuff isn't common in the US, it would be good to know that.  

"Lemon Thyme Shortbread (Makes about 20 fingers)

You can add all sorts of flavourings to shortbread, from vanilla and cocoa powder to hazelnuts and almonds. Herbs are good too: rosemary and lavender both work well, as does lemon thyme, which gives the biscuits a lovely delicate perfume.

340 g plain flour, plus extra for rolling
1/4 tsp fine sea salt
225 g unslated butter, softened, plus extra for greasing
140 g caster sugar, plus extra to sprinkle
2 tbsp finely chopped lemon thyme


Sift the flour into a bowl with the salt and set aside. Put the butter and sugar in a mixing bowl and beat with an electric mixer until smooth and creamy. 
Turn the mixer to its lowest setting and, with the motor running, add the lemon thyme, then the flour, a little at a time. Stop mixing as soon as the dough comes together. Shape into a flattened ball, wrap in cling film and chill for at least 20 minutes. 
Meanwhile, preheat the oven to 180 deg C/ Gas 4.
For shortbread fingers, gently pack the dough into a lightly buttered Swiss roll tin (roughly 30 x 20 cm). Score the surface to mark out the fingers and prick all over with a fork. If you want to make circular biscuits, roll out the dough on a lightly floured board to 5-7 mmm thick, then stam out the rounds using a 6 cm cutter. Transfer to 2 lightly buttered baking sheets, leaving a little space between each biscuit, then prick them with a fork.
Bake for 15-20 minutes until pale golden, checking often as ovens vary and the shortbread can easily burn. Cool in the tin or on the sheet until firm, then transfer to a wire rack to cool completely. 
Sprinkle with caster sugar, if you like, and store in an airtight container."


Source: Gordon Ramsay's Ultimate Cookery Course, pg. 279
Lemon zest and thyme would be a perfect substitute for lemon thyme. Lemon thyme is an entirely different species from regular thyme, but the name is very apropos. Figure maybe 1 part finely grated zest to 3 parts thyme. As with all herbs, the ideal amount is really very subjective. Start with half of what your recipe calls for, taste your dough and guess from there. You won't really know until you taste the baked shortbread, but you won't be terribly off either.

As a general rule of thumb, 3 parts of fresh herbs equals approximately 1 part of the same herb dried (whole leaf). If your dried herb is ground (or rubbed), figure just over half of the dried, whole leaf amount. Know that ground herbs and spices lose flavor quickly (as in they are pretty tasteless after a matter of a few weeks).

It means nothing, but I hate lavender: Is there a typical ratio for Herbes de Provence? :)