This happened to me last night...I was planning on what to bake tonight, and came across a Pecan Pie recipe, something I'd been meaning to give a go for a while...it was for a 23cm tin, a size I don't (currently) have... My normal approach is to work out the area of the tin, and then apply ratios, but thinking about it, for flan tins specifically, it's a little more complex than that.
I have 4 flan tin sizes;
- 12 x 10cm diameter tins, with a depth of 18mm
- 4 x 12cm diameter tins, with a depth of 23mm
- 1 x 20cm diameter tin, with a depth of 33mm
- 1 x 30cm diameter tin, with a depth of 34mm
If we just worked on area of the base of the tin (and I use Google to do the maths), you get ratios compared to a 23cm tin of;
- 10cm tin - 0.20
- 12cm tin - 0.28
- 20cm tin - 0.75
- (23cm tin) - 1.00
- 30cm tin - 1.70
This sort of thing works for cakes, as the area is equal to the volume...however for flan tins, the surface area for pastry is not quite the same...the effective diameter of the circles of pastry you need to roll is the base area plus the sides (so, for a 12cm tin, the effective diameter is 12 + 2.3 + 2.3); using these larger diameters, for the pastry the ration are;
- 10cm tin - 0.20
- 12cm tin - 0.31
- 20cm tin - 0.80
- (23cm tin) - 1.00
- 30cm tin - 1.56
So where does this leave me? Well, there is a decent chance I'll pop into Lakeland and get myself a 23cm tin, however another option is to make 3 x 12cm tarts, or slightly boost the pastry volumes and make 4 (there is always some cut-off anyway!). The biggest problem with scaling recipes is that there are some ingredients that you can't add 20% more to easily (the most obvious being eggs...the recipe I have uses 3 in the filling, and a yolk in the pastry)...I guess this is why we end up with so many tins!