Heat oven to 190C/170C fan/gas 5. Melt
the butter in a pan, stir in the flour and
cook for 2 mins. Add the onion and garlic
and cook for 3-5 mins until soft. Add the
mascarpone, then slowly add the spinach
liquid, stirring until smooth. Cook for
4-5 mins until the sauce thickens.
Stir in the cheddar, jalapeños, celery salt,
paprika and spinach. Transfer to a baking
dish and bake for 40 mins until golden.