The most favoured gluten/grain free flour substitute in my kitchen is almond meal. It is finely ground blanched almonds and in some countries, it is called almond flour. It has a slightly sweet flavour so you don’t have to add as much sweetener when baking with it. All kinds of nuts can be ground down to make a meal and are excellent for raw cheesecake or pie bases. Nut and seeds meals/flours are all best stored in airtight containers in the fridge or freezer to prevent them going rancid.