For the lemon curd, whisk the eggs together in a small saucepan. Add the lemon zest, lemon juice, butter, sugar and cornflour. Stir over a low heat until the curd thickens. Pour into a bowl and then chill in the fridge.
For the sponge, preheat the oven to 180C/350F/Gas 4. Spray the muffin tin with cake release spray or grease with butter. Line the bottom of the trays with small circles of baking parchment.
Put the baking spread and sugar in a freestanding mixer and cream together until smooth and pale. Mix in the eggs, then fold in the flour, salt, baking powder, thyme and lemon zest.
Fill each hole of the muffin tin until three-quarters full (it’s easiest to use an ice cream scoop, if you have one). Bake for 15-20 minutes, or until golden-brown and springy to the touch.
Allow the cakes to cool in the tins, then remove and place on wire racks to cool completely.
For the syrup, heat the caster sugar, thyme, lemon zest and juice in a small saucepan until the sugar is dissolved and a syrup forms.
Using a fork or skewer, pierce the sponges then use a pastry brush to brush the warm syrup over the cakes.
For the topping, mix any remaining syrup with the sugar and lemon zest. Drizzle it over the tops of the mini cakes to create the classic lemon drizzle topping.
For the filling, use an electric whisk to cream the butter and sugar together. Stir in the mascarpone and then fold in the whipped cream. Spoon the filling into a piping fitted with a small round nozzle.
Slice the cakes in half and pipe small rounds on top of the bottom half of each cake. Spread the lemon curd on the top halves and then place on top of the creamed bases.
Top with the candied lemon slices and a few thyme leaves and arrange on a serving plate or cake stand.