Preheat the oven to 350°F. Line a 9x13 baking pan with a sling of parchment paper with at least an inch overhang on two sides.

In a medium bowl, sift together the sweet rice flour, oat flour, millet flour, xanthan gum, baking soda, baking powder and salt. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment or a bowl with a hand mixer, cream together the butter and sugar over medium speed until light and fluffy, about 3 minutes.

With the mixer on low-speed, add the eggs one at a time, mixing after each one.

Add the vanilla extract, mixing until just combined.

Keeping the speed on low, slowly add the dry ingredients in two batches, adding the milk in between, mixing until just combined.

Pour the batter into the prepared baking pan and use a rubber spatula to spread it into an even layer.

Press the raspberries evenly into the cake, then use a spatula to cover the raspberries with batter.

Bake for 40-50 minutes until the cake springs back when pressed in the middle and a toothpick comes out dry or with a few moist crumbs.

Remove from oven and let cool for at least 30 minutes in the pan. Use the parchment paper to lift the cake out of the pan to a cooling rack to cool completely.

Meanwhile prepare the frosting as written below.

Once the cake is completely cool, use an offset spatula to spread the frosting over the cake. Dust with reserved raspberry dust, if desired. Slice into 24 pieces (4 x 6) and serve. Keep any leftovers in an airtight container in the fridge for up to three days.

Reserve 1 tablespoon of the ground freeze-dried raspberries.

In the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese until smooth over medium speed. Add the butter and cream together over medium speed, scraping the sides as you go.

With the mixer on low, slowly add the powdered sugar, remaining ground freeze-dried raspberries, vanilla extract, and salt. Beat until smooth.