Place the rice flour, polenta, butter and Parmesan in a food processor and whizz until the mixture resembles fine breadcrumbs. Alternatively, mix together the rice flour and polenta in a bowl. Add the butter and rub in with the fingertips until the mix resembles fine breadcrumbs. Stir in the Parmesan.
Add the egg yolk and enough cold water to form a soft but not sticky dough. Wrap in clingfilm and chill for 30 minutes.
Roll the dough out on a surface lightly dusted with rice flour and use a 10 cm (4 inch) plain cutter to stamp out 4 rounds, rerolling the trimmings as necessary.
Put the pastry rounds on a baking sheet lightly dusted with rice flour, then spoon over the onion marmalade or chutney, dot with the goats' cheese and sprinkle over the thyme.
Place in a preheated oven, 200°C (400°F), Gas Mark 6, for 12–15 minutes until golden. Serve with a spinach and rocket leaf salad, if liked.