Preheat oven to 180C and line the bottom of a square 20cm tin.
Melt the butter, then tip in the biscuit crumbs and sugar, mix thoroughly, then press into the bottom of the tin while still warm. Bake for 10 minutes.
Whisk together the eggs and sugar until light and the sugar has dissolved.
Add citrus juice, zest and tequila.
Then add the flour and whisk until smooth.
Pour the filling mix over the baked biscuit base then put it back in the oven for around 25 minutes until the top starts to colour.
Leave to cool in the tin for 30 minutes, then remove to a rack and chill for 2 hours.
Once chilled through, cut into squares and dust with icing sugar, then serve.
Magarita Sour
Add all ingredients into a shaker.
Dry shake for 5 seconds.
Add cubed ice and shake for 10 seconds.
Sugar the rim of a glass, fill with cubed ice and strain the sour into the glass.