Place peanuts in a single layer on a shallow baking pan. Roast at 350°F (180°C) for about 12 to 15 minutes until just lightly brown. Remove and allow peanuts to cool.
Grind peanuts in a food processor to as fine as possible.
Pour into a large bowl. Mix in rice flour, powdered sugar, and salt. Pour in oil and mix well. Peanut and flour mixture should come together.
Shape dough into 1-inch balls. Flatten slightly before placing onto parchment lined baking pan.
Brush top of cookie with egg wash.
Bake in 375°F (190°C) oven for approximately 18 minutes.
Remove and cool in pan for 10 minutes.
Transfer onto wire rack to cool completely. Store in an air tight jar.